[llvm] [CGP] Drop nneg flag when moving zext past instruction (PR #72103)
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Mon Nov 13 03:15:52 PST 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
Fix the issue by not reusing the zext at all. The code already handles creation of new zexts if more than one is needed. Always use that code-path instead of trying to reuse the old zext in some case. (Alternatively we could also drop poison-generating flags on the old zext, but it seems cleaner to not reuse it at all, especially if it's not always possible anyway.)
Fixes https://github.com/llvm/llvm-project/issues/72046.
---
Full diff: https://github.com/llvm/llvm-project/pull/72103.diff
5 Files Affected:
- (modified) llvm/lib/CodeGen/CodeGenPrepare.cpp (+12-26)
- (modified) llvm/test/Transforms/CodeGenPrepare/X86/multi-extension.ll (+2-2)
- (added) llvm/test/Transforms/CodeGenPrepare/X86/pr72046.ll (+19)
- (modified) llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll (+1-1)
- (modified) llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll (+1-1)
``````````diff
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index fa0c753bff2f073..07dc718ee3a38c3 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -4568,8 +4568,6 @@ Value *TypePromotionHelper::promoteOperandForOther(
// Step #2.
TPT.replaceAllUsesWith(Ext, ExtOpnd);
// Step #3.
- Instruction *ExtForOpnd = Ext;
-
LLVM_DEBUG(dbgs() << "Propagate Ext to operands\n");
for (int OpIdx = 0, EndOpIdx = ExtOpnd->getNumOperands(); OpIdx != EndOpIdx;
++OpIdx) {
@@ -4597,33 +4595,21 @@ Value *TypePromotionHelper::promoteOperandForOther(
}
// Otherwise we have to explicitly sign extend the operand.
- // Check if Ext was reused to extend an operand.
- if (!ExtForOpnd) {
- // If yes, create a new one.
- LLVM_DEBUG(dbgs() << "More operands to ext\n");
- Value *ValForExtOpnd = IsSExt ? TPT.createSExt(Ext, Opnd, Ext->getType())
- : TPT.createZExt(Ext, Opnd, Ext->getType());
- if (!isa<Instruction>(ValForExtOpnd)) {
- TPT.setOperand(ExtOpnd, OpIdx, ValForExtOpnd);
- continue;
- }
- ExtForOpnd = cast<Instruction>(ValForExtOpnd);
- }
+ Value *ValForExtOpnd = IsSExt
+ ? TPT.createSExt(ExtOpnd, Opnd, Ext->getType())
+ : TPT.createZExt(ExtOpnd, Opnd, Ext->getType());
+ TPT.setOperand(ExtOpnd, OpIdx, ValForExtOpnd);
+ Instruction *InstForExtOpnd = dyn_cast<Instruction>(ValForExtOpnd);
+ if (!InstForExtOpnd)
+ continue;
+
if (Exts)
- Exts->push_back(ExtForOpnd);
- TPT.setOperand(ExtForOpnd, 0, Opnd);
+ Exts->push_back(InstForExtOpnd);
- // Move the sign extension before the insertion point.
- TPT.moveBefore(ExtForOpnd, ExtOpnd);
- TPT.setOperand(ExtOpnd, OpIdx, ExtForOpnd);
- CreatedInstsCost += !TLI.isExtFree(ExtForOpnd);
- // If more sext are required, new instructions will have to be created.
- ExtForOpnd = nullptr;
- }
- if (ExtForOpnd == Ext) {
- LLVM_DEBUG(dbgs() << "Extension is useless now\n");
- TPT.eraseInstruction(Ext);
+ CreatedInstsCost += !TLI.isExtFree(InstForExtOpnd);
}
+ LLVM_DEBUG(dbgs() << "Extension is useless now\n");
+ TPT.eraseInstruction(Ext);
return ExtOpnd;
}
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/multi-extension.ll b/llvm/test/Transforms/CodeGenPrepare/X86/multi-extension.ll
index cc8e99176bf6e12..d09193e75f99742 100644
--- a/llvm/test/Transforms/CodeGenPrepare/X86/multi-extension.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/multi-extension.ll
@@ -10,8 +10,8 @@ declare void @bar(i64)
; %or is reachable by both a sext and zext that are going to be promoted.
; It ensures correct operation on PromotedInsts.
-; CHECK: %promoted = trunc i32 %or to i16
-; CHECK-NEXT: %c = sext i16 %promoted to i64
+; CHECK: %promoted3 = trunc i32 %or to i16
+; CHECK-NEXT: %c = sext i16 %promoted3 to i64
define i32 @foo(i16 %kkk) {
entry:
%t4 = load i16, ptr @b, align 2
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/pr72046.ll b/llvm/test/Transforms/CodeGenPrepare/X86/pr72046.ll
new file mode 100644
index 000000000000000..d75e5632ebb2e58
--- /dev/null
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/pr72046.ll
@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -S -codegenprepare -mtriple=x86_64-unknown-unknown < %s | FileCheck %s
+
+; Make sure the nneg flag is dropped when lshr and zext are interchanged.
+define i8 @get(ptr %box, i32 %in) {
+; CHECK-LABEL: define i8 @get(
+; CHECK-SAME: ptr [[BOX:%.*]], i32 [[IN:%.*]]) {
+; CHECK-NEXT: [[PROMOTED:%.*]] = zext i32 [[IN]] to i64
+; CHECK-NEXT: [[SHR:%.*]] = lshr i64 [[PROMOTED]], 24
+; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i8, ptr [[BOX]], i64 [[SHR]]
+; CHECK-NEXT: [[RES:%.*]] = load i8, ptr [[ARRAYIDX]], align 1
+; CHECK-NEXT: ret i8 [[RES]]
+;
+ %shr = lshr i32 %in, 24
+ %idxprom = zext nneg i32 %shr to i64
+ %arrayidx = getelementptr inbounds i8, ptr %box, i64 %idxprom
+ %res = load i8, ptr %arrayidx, align 1
+ ret i8 %res
+}
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll b/llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll
index 081c6742ede8c91..0ff35e1406de2bf 100644
--- a/llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll
@@ -1,7 +1,7 @@
; RUN: opt < %s -codegenprepare -S -mtriple=x86_64-unknown-unknown | FileCheck %s --match-full-lines
; Make sure the promoted trunc doesn't get a debug location associated.
-; CHECK: %promoted = trunc i32 %or to i16
+; CHECK: %promoted3 = trunc i32 %or to i16
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.13.0"
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll b/llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll
index 0b4f830ff3e7d99..f293d46ed6f74c6 100644
--- a/llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/promoted-zext-debugloc.ll
@@ -1,7 +1,7 @@
; RUN: opt < %s -codegenprepare -S -mtriple=x86_64-unknown-unknown | FileCheck %s --match-full-lines
; Make sure the promoted zext doesn't get a debug location associated.
-; CHECK: %promoted = zext i8 %t to i64
+; CHECK: %promoted1 = zext i8 %t to i64
define void @patatino(ptr %p, ptr %q, i32 %b, ptr %addr) !dbg !6 {
entry:
``````````
</details>
https://github.com/llvm/llvm-project/pull/72103
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