[llvm] 2b98b8e - fix bug for useless malloc elimination in CodeGenPrepare

[Ruobing Han via llvm-commits]

Author: Ruobing Han
Date: 2022-07-20T16:29:51Z
New Revision: 2b98b8e8fba1f7a7d11d099ecf2ebe1adc55b5aa

URL: https://github.com/llvm/llvm-project/commit/2b98b8e8fba1f7a7d11d099ecf2ebe1adc55b5aa
DIFF: https://github.com/llvm/llvm-project/commit/2b98b8e8fba1f7a7d11d099ecf2ebe1adc55b5aa.diff

LOG: fix bug for useless malloc elimination in CodeGenPrepare

Put AllocationFn check before I->willReturn can allow CodeGenPrepare to remove useless malloc instruction

Differential Revision: https://reviews.llvm.org/D130126

Added: 
    llvm/test/Transforms/CodeGenPrepare/dead-allocation.ll

Modified: 
    llvm/lib/Transforms/Utils/Local.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index b203259db1c68..9b1bb93b29153 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -439,6 +439,9 @@ bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
     return true;
   }
 
+  if (isAllocationFn(I, TLI) && isAllocRemovable(cast<CallBase>(I), TLI))
+    return true;
+
   if (!I->willReturn())
     return false;
 
@@ -489,9 +492,6 @@ bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
     }
   }
 
-  if (isAllocationFn(I, TLI) && isAllocRemovable(cast<CallBase>(I), TLI))
-    return true;
-
   if (CallInst *CI = isFreeCall(I, TLI))
     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
       return C->isNullValue() || isa<UndefValue>(C);

diff  --git a/llvm/test/Transforms/CodeGenPrepare/dead-allocation.ll b/llvm/test/Transforms/CodeGenPrepare/dead-allocation.ll
new file mode 100644
index 0000000000000..65d775f4a5ccf
--- /dev/null
+++ b/llvm/test/Transforms/CodeGenPrepare/dead-allocation.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; Eliminate the dead allocation instruction
+; RUN: opt -codegenprepare < %s -S | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7--linux-gnueabihf"
+
+ at .str = private unnamed_addr constant [2 x i8] c"a\00", align 1
+
+define void @func() {
+; CHECK-LABEL: @func(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %0 = tail call noalias noundef nonnull dereferenceable(32) ptr @_Znwm(i64 noundef 32)
+  %1 = icmp ugt ptr %0, @.str
+  tail call void @llvm.assume(i1 %1)
+  ret void
+}
+
+declare noundef nonnull ptr @_Znwm(i64 noundef) local_unnamed_addr
+declare void @llvm.assume(i1 noundef)