From b85257e1051d6b7dd3de6f4738fbb43a0528f8fb Mon Sep 17 00:00:00 2001
From: Damyan Pepper <damyanp@microsoft.com>
Date: Thu, 1 Oct 2026 17:05:11 -0700
Subject: [PATCH 1/2] Limit non-local call dependency walks in
 MemoryDependenceAnalysis

GVN queries non-local dependencies for read-only calls (e.g.
dx.op.createHandleForLib). When clobbers sit on conditional paths the
walk visits every block back to the function entry, making GVN
quadratic on large shaders. Once a non-Def dependency is found the
result is unusable by GVN, so stop scanning after 100 blocks and mark
the rest Unknown. Output is unchanged; on a Dawn-generated repro total
compile time drops from ~46s to ~8s.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 docs/ReleaseNotes.md                          |   3 +
 lib/Analysis/MemoryDependenceAnalysis.cpp     |  32 ++
 .../DXC/Passes/GVN/nonlocal-call-dep-limit.ll | 487 ++++++++++++++++++
 3 files changed, 522 insertions(+)
 create mode 100644 tools/clang/test/DXC/Passes/GVN/nonlocal-call-dep-limit.ll

diff --git a/docs/ReleaseNotes.md b/docs/ReleaseNotes.md
index 4da2a4f644..6581c5001a 100644
--- a/docs/ReleaseNotes.md
+++ b/docs/ReleaseNotes.md
@@ -67,6 +67,9 @@ line upon naming the release. Refer to previous for appropriate section names.
 
 - Fixed an optimizer crash when scalarizing an out-of-bounds vector access
   [#8940](https://github.com/microsoft/DirectXShaderCompiler/issues/8940).
+- Reduced GVN compile time on large shaders with many resource accesses by
+  limiting non-local memory dependency walks for calls once a result is known
+  to be unusable; generated code is unchanged.
 
 ### Upcoming Preview Release
 
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 5c337fe4cf..135a14af90 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -54,6 +54,15 @@ static const unsigned int BlockScanLimit = 500;
 // Limit on the number of memdep results to process.
 static const unsigned int NumResultsLimit = 100;
 
+// HLSL Change Begin - Limit non-local call dependency walks.
+// Without a limit, a query for a read-only call whose clobbers are all on
+// conditional paths walks every block back to the function entry, making GVN
+// quadratic on large shaders with many inlined call sites. The limit is only
+// applied once the walk has found a non-Def dependency (see
+// getNonLocalCallDependency).
+static const unsigned int CallBlockNumberLimit = 100;
+// HLSL Change End
+
 char MemoryDependenceAnalysis::ID = 0;
 
 // Register this pass...
@@ -785,6 +794,18 @@ MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) {
 
   SmallPtrSet<BasicBlock*, 64> Visited;
 
+  // HLSL Change Begin - Track whether a non-Def dependency has been found.
+  auto IsNonDefDep = [](const MemDepResult &R) {
+    return !R.isNonLocal() && !R.isDef() && !R.isDirty();
+  };
+  bool FoundNonDefDep = false;
+  for (const NonLocalDepEntry &E : Cache)
+    if (IsNonDefDep(E.getResult())) {
+      FoundNonDefDep = true;
+      break;
+    }
+  // HLSL Change End
+
   unsigned NumSortedEntries = Cache.size();
   DEBUG(AssertSorted(Cache));
 
@@ -833,6 +854,16 @@ MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) {
     // Find out if this block has a local dependency for QueryInst.
     MemDepResult Dep;
 
+    // HLSL Change Begin - Once the walk has visited too many blocks and has
+    // already found a dependency that is not a Def (a clobber or unknown),
+    // stop scanning and conservatively mark this and any remaining blocks
+    // Unknown. Such a result already cannot prove the query redundant, so
+    // scanning further only costs compile time. Unknown is not NonLocal, so
+    // predecessors are not added to the worklist.
+    if (FoundNonDefDep && Visited.size() > CallBlockNumberLimit) {
+      Dep = MemDepResult::getUnknown();
+    } else
+    // HLSL Change End
     if (ScanPos != DirtyBB->begin()) {
       Dep = getCallSiteDependencyFrom(QueryCS, isReadonlyCall,ScanPos, DirtyBB);
     } else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) {
@@ -853,6 +884,7 @@ MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) {
     // If the block has a dependency (i.e. it isn't completely transparent to
     // the value), remember the association!
     if (!Dep.isNonLocal()) {
+      FoundNonDefDep |= IsNonDefDep(Dep); // HLSL Change
       // Keep the ReverseNonLocalDeps map up to date so we can efficiently
       // update this when we remove instructions.
       if (Instruction *Inst = Dep.getInst())
diff --git a/tools/clang/test/DXC/Passes/GVN/nonlocal-call-dep-limit.ll b/tools/clang/test/DXC/Passes/GVN/nonlocal-call-dep-limit.ll
new file mode 100644
index 0000000000..bc4fa9de92
--- /dev/null
+++ b/tools/clang/test/DXC/Passes/GVN/nonlocal-call-dep-limit.ll
@@ -0,0 +1,487 @@
+; RUN: %dxopt %s -basicaa -gvn -S | FileCheck %s
+
+; Non-local dependency walks for read-only calls in MemoryDependenceAnalysis
+; stop after visiting a limited number of blocks (100), but only once a
+; clobbering dependency has been found, since such a result can no longer prove
+; the call redundant. Walks that only find Defs are not limited, so GVN still
+; removes redundant calls whose dominating definition is far away.
+
+declare i32 @f(i32*) readonly
+declare void @g(i32*)
+
+; The dominating call is more than 100 blocks away, but with no clobbers in
+; between the limit does not apply and GVN removes the second call.
+; CHECK-LABEL: @far_def(
+; CHECK: %a = call i32 @f(i32* %p)
+; CHECK-NOT: call i32 @f(
+; CHECK: add i32 %a, %a
+define i32 @far_def(i32* %p) {
+entry:
+  %a = call i32 @f(i32* %p)
+  br label %c0
+c0:
+  br label %c1
+c1:
+  br label %c2
+c2:
+  br label %c3
+c3:
+  br label %c4
+c4:
+  br label %c5
+c5:
+  br label %c6
+c6:
+  br label %c7
+c7:
+  br label %c8
+c8:
+  br label %c9
+c9:
+  br label %c10
+c10:
+  br label %c11
+c11:
+  br label %c12
+c12:
+  br label %c13
+c13:
+  br label %c14
+c14:
+  br label %c15
+c15:
+  br label %c16
+c16:
+  br label %c17
+c17:
+  br label %c18
+c18:
+  br label %c19
+c19:
+  br label %c20
+c20:
+  br label %c21
+c21:
+  br label %c22
+c22:
+  br label %c23
+c23:
+  br label %c24
+c24:
+  br label %c25
+c25:
+  br label %c26
+c26:
+  br label %c27
+c27:
+  br label %c28
+c28:
+  br label %c29
+c29:
+  br label %c30
+c30:
+  br label %c31
+c31:
+  br label %c32
+c32:
+  br label %c33
+c33:
+  br label %c34
+c34:
+  br label %c35
+c35:
+  br label %c36
+c36:
+  br label %c37
+c37:
+  br label %c38
+c38:
+  br label %c39
+c39:
+  br label %c40
+c40:
+  br label %c41
+c41:
+  br label %c42
+c42:
+  br label %c43
+c43:
+  br label %c44
+c44:
+  br label %c45
+c45:
+  br label %c46
+c46:
+  br label %c47
+c47:
+  br label %c48
+c48:
+  br label %c49
+c49:
+  br label %c50
+c50:
+  br label %c51
+c51:
+  br label %c52
+c52:
+  br label %c53
+c53:
+  br label %c54
+c54:
+  br label %c55
+c55:
+  br label %c56
+c56:
+  br label %c57
+c57:
+  br label %c58
+c58:
+  br label %c59
+c59:
+  br label %c60
+c60:
+  br label %c61
+c61:
+  br label %c62
+c62:
+  br label %c63
+c63:
+  br label %c64
+c64:
+  br label %c65
+c65:
+  br label %c66
+c66:
+  br label %c67
+c67:
+  br label %c68
+c68:
+  br label %c69
+c69:
+  br label %c70
+c70:
+  br label %c71
+c71:
+  br label %c72
+c72:
+  br label %c73
+c73:
+  br label %c74
+c74:
+  br label %c75
+c75:
+  br label %c76
+c76:
+  br label %c77
+c77:
+  br label %c78
+c78:
+  br label %c79
+c79:
+  br label %c80
+c80:
+  br label %c81
+c81:
+  br label %c82
+c82:
+  br label %c83
+c83:
+  br label %c84
+c84:
+  br label %c85
+c85:
+  br label %c86
+c86:
+  br label %c87
+c87:
+  br label %c88
+c88:
+  br label %c89
+c89:
+  br label %c90
+c90:
+  br label %c91
+c91:
+  br label %c92
+c92:
+  br label %c93
+c93:
+  br label %c94
+c94:
+  br label %c95
+c95:
+  br label %c96
+c96:
+  br label %c97
+c97:
+  br label %c98
+c98:
+  br label %c99
+c99:
+  br label %c100
+c100:
+  br label %c101
+c101:
+  br label %c102
+c102:
+  br label %c103
+c103:
+  br label %c104
+c104:
+  br label %c105
+c105:
+  br label %c106
+c106:
+  br label %c107
+c107:
+  br label %c108
+c108:
+  br label %c109
+c109:
+  br label %use
+use:
+  %b = call i32 @f(i32* %p)
+  %r = add i32 %a, %b
+  ret i32 %r
+}
+
+; The query in %use finds the clobber in %clob before walking the long path
+; through %c0..%c109, so the walk is cut off. The call is not redundant either
+; way.
+; CHECK-LABEL: @far_def_clobber(
+; CHECK: %a = call i32 @f(i32* %p)
+; CHECK: call void @g(i32* %p)
+; CHECK: %b = call i32 @f(i32* %p)
+; CHECK: add i32 %a, %b
+define i32 @far_def_clobber(i1 %cond, i32* %p) {
+entry:
+  %a = call i32 @f(i32* %p)
+  br i1 %cond, label %c0, label %clob
+clob:
+  call void @g(i32* %p)
+  br label %use
+c0:
+  br label %c1
+c1:
+  br label %c2
+c2:
+  br label %c3
+c3:
+  br label %c4
+c4:
+  br label %c5
+c5:
+  br label %c6
+c6:
+  br label %c7
+c7:
+  br label %c8
+c8:
+  br label %c9
+c9:
+  br label %c10
+c10:
+  br label %c11
+c11:
+  br label %c12
+c12:
+  br label %c13
+c13:
+  br label %c14
+c14:
+  br label %c15
+c15:
+  br label %c16
+c16:
+  br label %c17
+c17:
+  br label %c18
+c18:
+  br label %c19
+c19:
+  br label %c20
+c20:
+  br label %c21
+c21:
+  br label %c22
+c22:
+  br label %c23
+c23:
+  br label %c24
+c24:
+  br label %c25
+c25:
+  br label %c26
+c26:
+  br label %c27
+c27:
+  br label %c28
+c28:
+  br label %c29
+c29:
+  br label %c30
+c30:
+  br label %c31
+c31:
+  br label %c32
+c32:
+  br label %c33
+c33:
+  br label %c34
+c34:
+  br label %c35
+c35:
+  br label %c36
+c36:
+  br label %c37
+c37:
+  br label %c38
+c38:
+  br label %c39
+c39:
+  br label %c40
+c40:
+  br label %c41
+c41:
+  br label %c42
+c42:
+  br label %c43
+c43:
+  br label %c44
+c44:
+  br label %c45
+c45:
+  br label %c46
+c46:
+  br label %c47
+c47:
+  br label %c48
+c48:
+  br label %c49
+c49:
+  br label %c50
+c50:
+  br label %c51
+c51:
+  br label %c52
+c52:
+  br label %c53
+c53:
+  br label %c54
+c54:
+  br label %c55
+c55:
+  br label %c56
+c56:
+  br label %c57
+c57:
+  br label %c58
+c58:
+  br label %c59
+c59:
+  br label %c60
+c60:
+  br label %c61
+c61:
+  br label %c62
+c62:
+  br label %c63
+c63:
+  br label %c64
+c64:
+  br label %c65
+c65:
+  br label %c66
+c66:
+  br label %c67
+c67:
+  br label %c68
+c68:
+  br label %c69
+c69:
+  br label %c70
+c70:
+  br label %c71
+c71:
+  br label %c72
+c72:
+  br label %c73
+c73:
+  br label %c74
+c74:
+  br label %c75
+c75:
+  br label %c76
+c76:
+  br label %c77
+c77:
+  br label %c78
+c78:
+  br label %c79
+c79:
+  br label %c80
+c80:
+  br label %c81
+c81:
+  br label %c82
+c82:
+  br label %c83
+c83:
+  br label %c84
+c84:
+  br label %c85
+c85:
+  br label %c86
+c86:
+  br label %c87
+c87:
+  br label %c88
+c88:
+  br label %c89
+c89:
+  br label %c90
+c90:
+  br label %c91
+c91:
+  br label %c92
+c92:
+  br label %c93
+c93:
+  br label %c94
+c94:
+  br label %c95
+c95:
+  br label %c96
+c96:
+  br label %c97
+c97:
+  br label %c98
+c98:
+  br label %c99
+c99:
+  br label %c100
+c100:
+  br label %c101
+c101:
+  br label %c102
+c102:
+  br label %c103
+c103:
+  br label %c104
+c104:
+  br label %c105
+c105:
+  br label %c106
+c106:
+  br label %c107
+c107:
+  br label %c108
+c108:
+  br label %c109
+c109:
+  br label %use
+use:
+  %b = call i32 @f(i32* %p)
+  %r = add i32 %a, %b
+  ret i32 %r
+}

From 679e0e0c18bc198aacaa61ce543623196b6c010c Mon Sep 17 00:00:00 2001
From: Damyan Pepper <damyanp@microsoft.com>
Date: Thu, 1 Oct 2026 17:59:45 -0700
Subject: [PATCH 2/2] Fix formatting in memory dependence analysis

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 lib/Analysis/MemoryDependenceAnalysis.cpp | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 135a14af90..4f787995b7 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -863,16 +863,17 @@ MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) {
     if (FoundNonDefDep && Visited.size() > CallBlockNumberLimit) {
       Dep = MemDepResult::getUnknown();
     } else
-    // HLSL Change End
-    if (ScanPos != DirtyBB->begin()) {
-      Dep = getCallSiteDependencyFrom(QueryCS, isReadonlyCall,ScanPos, DirtyBB);
-    } else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) {
-      // No dependence found.  If this is the entry block of the function, it is
-      // a clobber, otherwise it is unknown.
-      Dep = MemDepResult::getNonLocal();
-    } else {
-      Dep = MemDepResult::getNonFuncLocal();
-    }
+      // HLSL Change End
+      if (ScanPos != DirtyBB->begin()) {
+        Dep = getCallSiteDependencyFrom(QueryCS, isReadonlyCall, ScanPos,
+                                        DirtyBB);
+      } else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) {
+        // No dependence found.  If this is the entry block of the function, it
+        // is a clobber, otherwise it is unknown.
+        Dep = MemDepResult::getNonLocal();
+      } else {
+        Dep = MemDepResult::getNonFuncLocal();
+      }
 
     // If we had a dirty entry for the block, update it.  Otherwise, just add
     // a new entry.