[llvm] Reapply [Metadata] Preserve MD_prof when merging instructions when one is missing. (PR #135418)
Snehasish Kumar via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 11 11:22:35 PDT 2025
https://github.com/snehasish created https://github.com/llvm/llvm-project/pull/135418
Preserve branch weight metadata when merging instructions if one of the instructions is missing metadata. This is similar in behaviour to what we do today for other types of metadata such as mmra, memprof and callsite metadata.
Also add a legality check when merging prof metadata based on instruction type. Without this check GVN PRE optimizations result in prof metadata on phi nodes which break the module verifier.
Build failure caught by https://lab.llvm.org/buildbot/#/builders/113/builds/6621
```
!9185 = !{!"branch_weights", i32 3912, i32 802}
Wrong number of operands
!9185 = !{!"branch_weights", i32 3912, i32 802}
fatal error: error in backend: Broken module found, compilation aborted!
```
Reverts #134200 with additional changes.
>From 96895580e46f4b44adc34e803d5b97344b1ba515 Mon Sep 17 00:00:00 2001
From: Snehasish Kumar <snehasishk at google.com>
Date: Fri, 11 Apr 2025 17:59:05 +0000
Subject: [PATCH] Reapply [Metadata] Preserve MD_prof when merging instructions
when one is missing.
Preserve branch weight metadata when merging instructions if one of the
instructions is missing metadata. This is similar in behaviour to what
we do today for other types of metadata such as mmra, memprof and
callsite metadata.
Also add a legality check when merging prof metadata based on
instruction type. Without this check GVN PRE optimizations result in
prof metadata on phi nodes which break the module verifier.
---
llvm/lib/IR/Metadata.cpp | 20 ++++++
llvm/lib/Transforms/Utils/Local.cpp | 19 ++++--
.../GVN/pre-invalid-prof-metadata.ll | 60 ++++++++++++++++++
...rect-call-branch-weights-preserve-hoist.ll | 62 ++++++++++++++++++
...irect-call-branch-weights-preserve-sink.ll | 63 +++++++++++++++++++
5 files changed, 218 insertions(+), 6 deletions(-)
create mode 100644 llvm/test/Transforms/GVN/pre-invalid-prof-metadata.ll
create mode 100644 llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-hoist.ll
create mode 100644 llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-sink.ll
diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index bc722c7ed3e31..8e78cd9cc573a 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -1223,6 +1223,26 @@ MDNode *MDNode::mergeDirectCallProfMetadata(MDNode *A, MDNode *B,
MDNode *MDNode::getMergedProfMetadata(MDNode *A, MDNode *B,
const Instruction *AInstr,
const Instruction *BInstr) {
+ // Check that it is legal to merge prof metadata based on the opcode.
+ auto IsLegal = [](const Instruction &I) -> bool {
+ switch (I.getOpcode()) {
+ case Instruction::Invoke:
+ case Instruction::Br:
+ case Instruction::Switch:
+ case Instruction::Call:
+ case Instruction::IndirectBr:
+ case Instruction::Select:
+ case Instruction::CallBr:
+ return true;
+ default:
+ return false;
+ }
+ };
+ if (AInstr && !IsLegal(*AInstr))
+ return nullptr;
+ if (BInstr && !IsLegal(*BInstr))
+ return nullptr;
+
if (!(A && B)) {
return A ? A : B;
}
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 2f3ea2266e07f..b3204da93049b 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -3353,9 +3353,10 @@ static void combineMetadata(Instruction *K, const Instruction *J,
case LLVMContext::MD_invariant_group:
// Preserve !invariant.group in K.
break;
- // Keep empty cases for mmra, memprof, and callsite to prevent them from
- // being removed as unknown metadata. The actual merging is handled
+ // Keep empty cases for prof, mmra, memprof, and callsite to prevent them
+ // from being removed as unknown metadata. The actual merging is handled
// separately below.
+ case LLVMContext::MD_prof:
case LLVMContext::MD_mmra:
case LLVMContext::MD_memprof:
case LLVMContext::MD_callsite:
@@ -3384,10 +3385,6 @@ static void combineMetadata(Instruction *K, const Instruction *J,
if (!AAOnly)
K->setMetadata(Kind, JMD);
break;
- case LLVMContext::MD_prof:
- if (!AAOnly && DoesKMove)
- K->setMetadata(Kind, MDNode::getMergedProfMetadata(KMD, JMD, K, J));
- break;
case LLVMContext::MD_noalias_addrspace:
if (DoesKMove)
K->setMetadata(Kind,
@@ -3434,6 +3431,16 @@ static void combineMetadata(Instruction *K, const Instruction *J,
K->setMetadata(LLVMContext::MD_callsite,
MDNode::getMergedCallsiteMetadata(KCallSite, JCallSite));
}
+
+ // Merge prof metadata.
+ // Handle separately to support cases where only one instruction has the
+ // metadata.
+ auto *JProf = J->getMetadata(LLVMContext::MD_prof);
+ auto *KProf = K->getMetadata(LLVMContext::MD_prof);
+ if (!AAOnly && (JProf || KProf)) {
+ K->setMetadata(LLVMContext::MD_prof,
+ MDNode::getMergedProfMetadata(KProf, JProf, K, J));
+ }
}
void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
diff --git a/llvm/test/Transforms/GVN/pre-invalid-prof-metadata.ll b/llvm/test/Transforms/GVN/pre-invalid-prof-metadata.ll
new file mode 100644
index 0000000000000..978bfd424ae52
--- /dev/null
+++ b/llvm/test/Transforms/GVN/pre-invalid-prof-metadata.ll
@@ -0,0 +1,60 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=gvn -S < %s | FileCheck %s
+
+; Make sure that performing PRE does not add prof metadata onto newly created
+; phi nodes.
+define fastcc ptr @foo(i8 %__pred.1.val) {
+; CHECK-LABEL: define fastcc ptr @foo(
+; CHECK-SAME: i8 [[__PRED_1_VAL:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: switch i64 0, label %[[SW_BB:.*]] [
+; CHECK-NEXT: i64 1, label %[[ENTRY_SW_BB26_CRIT_EDGE:.*]]
+; CHECK-NEXT: i64 0, label %[[ENTRY_SW_BB21_CRIT_EDGE:.*]]
+; CHECK-NEXT: ]
+; CHECK: [[ENTRY_SW_BB21_CRIT_EDGE]]:
+; CHECK-NEXT: [[DOTPRE:%.*]] = trunc i8 [[__PRED_1_VAL]] to i1
+; CHECK-NEXT: [[DOTPRE1:%.*]] = select i1 [[DOTPRE]], i64 0, i64 4
+; CHECK-NEXT: br label %[[SW_BB21:.*]]
+; CHECK: [[ENTRY_SW_BB26_CRIT_EDGE]]:
+; CHECK-NEXT: [[DOTPRE2:%.*]] = trunc i8 [[__PRED_1_VAL]] to i1
+; CHECK-NEXT: [[DOTPRE3:%.*]] = select i1 [[DOTPRE2]], i64 0, i64 4, !prof [[PROF0:![0-9]+]]
+; CHECK-NEXT: br label %[[SW_BB26:.*]]
+; CHECK: [[SW_BB]]:
+; CHECK-NEXT: [[L78:%.*]] = trunc i8 [[__PRED_1_VAL]] to i1
+; CHECK-NEXT: [[C79:%.*]] = select i1 [[L78]], i64 0, i64 4
+; CHECK-NEXT: br label %[[SW_BB21]]
+; CHECK: [[SW_BB21]]:
+; CHECK-NEXT: [[C84_PRE_PHI:%.*]] = phi i64 [ [[DOTPRE1]], %[[ENTRY_SW_BB21_CRIT_EDGE]] ], [ [[C79]], %[[SW_BB]] ]
+; CHECK-NEXT: [[L83_PRE_PHI:%.*]] = phi i1 [ [[DOTPRE]], %[[ENTRY_SW_BB21_CRIT_EDGE]] ], [ [[L78]], %[[SW_BB]] ]
+; CHECK-NEXT: br label %[[SW_BB26]]
+; CHECK: [[SW_BB26]]:
+; CHECK-NEXT: [[C89_PRE_PHI:%.*]] = phi i64 [ [[DOTPRE3]], %[[ENTRY_SW_BB26_CRIT_EDGE]] ], [ [[C84_PRE_PHI]], %[[SW_BB21]] ]
+; CHECK-NEXT: [[L88_PRE_PHI:%.*]] = phi i1 [ [[DOTPRE2]], %[[ENTRY_SW_BB26_CRIT_EDGE]] ], [ [[L83_PRE_PHI]], %[[SW_BB21]] ]
+; CHECK-NEXT: ret ptr null
+;
+entry:
+ switch i64 0, label %sw.bb [
+ i64 1, label %sw.bb26
+ i64 0, label %sw.bb21
+ ]
+
+sw.bb: ; preds = %entry
+ %l78 = trunc i8 %__pred.1.val to i1
+ %c79 = select i1 %l78, i64 0, i64 4
+ br label %sw.bb21
+
+sw.bb21: ; preds = %sw.bb, %entry
+ %l83 = trunc i8 %__pred.1.val to i1
+ %c84 = select i1 %l83, i64 0, i64 4
+ br label %sw.bb26
+
+sw.bb26: ; preds = %sw.bb21, %entry
+ %l88 = trunc i8 %__pred.1.val to i1
+ %c89 = select i1 %l88, i64 0, i64 4, !prof !0
+ ret ptr null
+}
+
+!0 = !{!"branch_weights", i32 3994, i32 883}
+;.
+; CHECK: [[PROF0]] = !{!"branch_weights", i32 3994, i32 883}
+;.
diff --git a/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-hoist.ll b/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-hoist.ll
new file mode 100644
index 0000000000000..d6058134f5285
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-hoist.ll
@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals --version 2
+; RUN: opt < %s -passes='simplifycfg<no-sink-common-insts;hoist-common-insts>' -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s --check-prefix=HOIST
+
+; Test case based on C++ code with manualy annotated !prof metadata.
+; This is to test that when calls to 'func1' from 'if.then' block
+; and 'if.else' block are hoisted, the branch_weights are merged and
+; attached to merged call rather than dropped.
+;
+; int func1(int a, int b) ;
+; int func2(int a, int b) ;
+
+; int func(int a, int b, bool c) {
+; int sum= 0;
+; if(c) {
+; sum += func1(a, b);
+; } else {
+; sum += func1(a, b);
+; sum -= func2(a, b);
+; }
+; return sum;
+; }
+define i32 @_Z4funciib(i32 %a, i32 %b, i1 %c) {
+; HOIST-LABEL: define i32 @_Z4funciib
+; HOIST-SAME: (i32 [[A:%.*]], i32 [[B:%.*]], i1 [[C:%.*]]) {
+; HOIST-NEXT: entry:
+; HOIST-NEXT: [[CALL:%.*]] = tail call i32 @_Z5func1ii(i32 [[A]], i32 [[B]]), !prof [[PROF0:![0-9]+]]
+; HOIST-NEXT: br i1 [[C]], label [[IF_END:%.*]], label [[IF_ELSE:%.*]]
+; HOIST: if.else:
+; HOIST-NEXT: [[CALL3:%.*]] = tail call i32 @_Z5func2ii(i32 [[A]], i32 [[B]])
+; HOIST-NEXT: [[SUB:%.*]] = sub i32 [[CALL]], [[CALL3]]
+; HOIST-NEXT: br label [[IF_END]]
+; HOIST: if.end:
+; HOIST-NEXT: [[SUM_0:%.*]] = phi i32 [ [[SUB]], [[IF_ELSE]] ], [ [[CALL]], [[ENTRY:%.*]] ]
+; HOIST-NEXT: ret i32 [[SUM_0]]
+;
+entry:
+ br i1 %c, label %if.then, label %if.else
+
+if.then: ; preds = %entry
+ %call = tail call i32 @_Z5func1ii(i32 %a, i32 %b)
+ br label %if.end
+
+if.else: ; preds = %entry
+ %call1 = tail call i32 @_Z5func1ii(i32 %a, i32 %b), !prof !0
+ %call3 = tail call i32 @_Z5func2ii(i32 %a, i32 %b)
+ %sub = sub i32 %call1, %call3
+ br label %if.end
+
+if.end: ; preds = %if.else, %if.then
+ %sum.0 = phi i32 [ %call, %if.then ], [ %sub, %if.else ]
+ ret i32 %sum.0
+}
+
+declare i32 @_Z5func1ii(i32, i32)
+
+declare i32 @_Z5func2ii(i32, i32)
+
+!0 = !{!"branch_weights", i32 10}
+
+;.
+; HOIST: [[PROF0]] = !{!"branch_weights", i32 10}
+;.
diff --git a/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-sink.ll b/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-sink.ll
new file mode 100644
index 0000000000000..c4aed5eb95888
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/merge-direct-call-branch-weights-preserve-sink.ll
@@ -0,0 +1,63 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals --version 2
+; RUN: opt < %s -passes='simplifycfg<sink-common-insts;no-hoist-common-insts>' -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s --check-prefix=SINK
+
+
+; Test case based on the following C++ code with manualy annotated !prof metadata.
+; This is to test that when calls to 'func1' from 'if.then' and 'if.else' are
+; sinked, the branch weights are merged and attached to sinked call.
+;
+; int func1(int a, int b) ;
+; int func2(int a, int b) ;
+
+; int func(int a, int b, bool c) {
+; int sum = 0;
+; if (c) {
+; sum += func1(a,b);
+; } else {
+; b -= func2(a,b);
+; sum += func1(a,b);
+; }
+; return sum;
+; }
+
+define i32 @_Z4funciib(i32 %a, i32 %b, i1 %c) {
+; SINK-LABEL: define i32 @_Z4funciib
+; SINK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]], i1 [[C:%.*]]) {
+; SINK-NEXT: entry:
+; SINK-NEXT: br i1 [[C]], label [[IF_END:%.*]], label [[IF_ELSE:%.*]]
+; SINK: if.else:
+; SINK-NEXT: [[CALL1:%.*]] = tail call i32 @_Z5func2ii(i32 [[A]], i32 [[B]])
+; SINK-NEXT: [[SUB:%.*]] = sub i32 [[B]], [[CALL1]]
+; SINK-NEXT: br label [[IF_END]]
+; SINK: if.end:
+; SINK-NEXT: [[SUB_SINK:%.*]] = phi i32 [ [[SUB]], [[IF_ELSE]] ], [ [[B]], [[ENTRY:%.*]] ]
+; SINK-NEXT: [[CALL2:%.*]] = tail call i32 @_Z5func1ii(i32 [[A]], i32 [[SUB_SINK]]), !prof [[PROF0:![0-9]+]]
+; SINK-NEXT: ret i32 [[CALL2]]
+;
+entry:
+ br i1 %c, label %if.then, label %if.else
+
+if.then: ; preds = %entry
+ %call = tail call i32 @_Z5func1ii(i32 %a, i32 %b), !prof !0
+ br label %if.end
+
+if.else: ; preds = %entry
+ %call1 = tail call i32 @_Z5func2ii(i32 %a, i32 %b)
+ %sub = sub i32 %b, %call1
+ %call2 = tail call i32 @_Z5func1ii(i32 %a, i32 %sub)
+ br label %if.end
+
+if.end: ; preds = %if.else, %if.then
+ %sum.0 = phi i32 [ %call, %if.then ], [ %call2, %if.else ]
+ ret i32 %sum.0
+}
+
+declare i32 @_Z5func1ii(i32, i32)
+
+declare i32 @_Z5func2ii(i32, i32)
+
+!0 = !{!"branch_weights", i32 10}
+
+;.
+; SINK: [[PROF0]] = !{!"branch_weights", i32 10}
+;.
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