[PATCH] D22644: [GVNHoist] Don't clone allocas (PR28606)

[Hans Wennborg via llvm-commits]

hans updated this revision to Diff 64951.
hans marked an inline comment as done.
hans added a comment.

Address David's comment.


https://reviews.llvm.org/D22644

Files:
  lib/Transforms/Scalar/GVNHoist.cpp
  test/Transforms/GVN/hoist-pr28606.ll

Index: test/Transforms/GVN/hoist-pr28606.ll
===================================================================
--- /dev/null
+++ test/Transforms/GVN/hoist-pr28606.ll
@@ -0,0 +1,46 @@
+; RUN: opt -gvn-hoist -S < %s | FileCheck %s
+
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+%struct.S = type { i8* }
+
+declare void @f(<{ %struct.S }>* inalloca)
+
+
+; Check that we don't clone the %x alloca and insert it in the live range of
+; %argmem, which would break the inalloca contract.
+;
+; CHECK-LABEL: @test
+; CHECK: alloca i8
+; CHECK: stacksave
+; CHECK: alloca inalloca
+; CHECK-NOT: alloca i8
+; CHECK: stackrestore
+
+define void @test(i1 %b) {
+entry:
+  %x = alloca i8
+  %inalloca.save = call i8* @llvm.stacksave()
+  %argmem = alloca inalloca <{ %struct.S }>, align 4
+  %0 = getelementptr inbounds <{ %struct.S }>, <{ %struct.S }>* %argmem, i32 0, i32 0
+  br i1 %b, label %true, label %false
+
+true:
+  %p = getelementptr inbounds %struct.S, %struct.S* %0, i32 0, i32 0
+  store i8* %x, i8** %p, align 4
+  br label %exit
+
+false:
+  %p2 = getelementptr inbounds %struct.S, %struct.S* %0, i32 0, i32 0
+  store i8* %x, i8** %p2, align 4
+  br label %exit
+
+exit:
+  call void @f(<{ %struct.S }>* inalloca %argmem)
+  call void @llvm.stackrestore(i8* %inalloca.save)
+  ret void
+}
+
+declare i8* @llvm.stacksave()
+declare void @llvm.stackrestore(i8*)
Index: lib/Transforms/Scalar/GVNHoist.cpp
===================================================================
--- lib/Transforms/Scalar/GVNHoist.cpp
+++ lib/Transforms/Scalar/GVNHoist.cpp
@@ -600,6 +600,12 @@
     if (Val && !allOperandsAvailable(Val, HoistPt))
       return false;
 
+    // Don't copy allocas: it can either pessimize the program by turning a
+    // static alloca into a dynamic one, or worse it could break the program if
+    // it's inserted in the live range of an inalloca.
+    if (Val && isa<AllocaInst>(Val))
+      return false;
+
     // Copy the gep before moving the ld/st.
     Instruction *ClonedGep = Gep->clone();
     ClonedGep->insertBefore(HoistPt->getTerminator());


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