GVH-hoist: only clone GEPs (PR28606)

Do not clone stored values unless they are GEPs that are special cased to avoid
hoisting them without hoisting their associated ld/st.

Differential revision: https://reviews.llvm.org/D22652

llvm-svn: 276358

3 files changed, 59 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVNHoist.cpp b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
index cf2181b34eb..ad373ba542e 100644
--- a/llvm/lib/Transforms/Scalar/GVNHoist.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
@@ -584,21 +584,14 @@ public:
     if (auto *St = dyn_cast<StoreInst>(Repl)) {
       Gep = dyn_cast<GetElementPtrInst>(St->getPointerOperand());
       Val = dyn_cast<Instruction>(St->getValueOperand());
+      // Check that the stored value is available.
+      if (Val && !isa<GetElementPtrInst>(Val) &&
+          !DT->dominates(Val->getParent(), HoistPt))
+        return false;
     }
 
-    if (!Gep)
-      return false;
-
-    // PHIs may only be inserted at the start of a block.
-    if (Val && isa<PHINode>(Val))
-      return false;
-
     // Check whether we can compute the Gep at HoistPt.
-    if (!allOperandsAvailable(Gep, HoistPt))
-      return false;
-
-    // Also check that the stored value is available.
-    if (Val && !allOperandsAvailable(Val, HoistPt))
+    if (!Gep || !allOperandsAvailable(Gep, HoistPt))
       return false;
 
     // Copy the gep before moving the ld/st.
@@ -618,8 +611,8 @@ public:
     }
     Repl->replaceUsesOfWith(Gep, ClonedGep);
 
-    // Also copy Val.
-    if (Val) {
+    // Also copy Val when it is a GEP.
+    if (Val && isa<GetElementPtrInst>(Val)) {
       Instruction *ClonedVal = Val->clone();
       ClonedVal->insertBefore(HoistPt->getTerminator());
       // Conservatively discard any optimization hints, they may differ on the
diff --git a/llvm/test/Transforms/GVN/hoist-pr28606.ll b/llvm/test/Transforms/GVN/hoist-pr28606.ll
new file mode 100644
index 00000000000..2c588283ea9
--- /dev/null
+++ b/llvm/test/Transforms/GVN/hoist-pr28606.ll
@@ -0,0 +1,50 @@
+; 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 that store instructions are hoisted.
+; CHECK: store i8
+; CHECK-NOT: store 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*)
diff --git a/llvm/test/Transforms/GVN/pr28626.ll b/llvm/test/Transforms/GVN/pr28626.ll
index 742d968be36..7930e694825 100644
--- a/llvm/test/Transforms/GVN/pr28626.ll
+++ b/llvm/test/Transforms/GVN/pr28626.ll
@@ -38,5 +38,5 @@ if.end6:                                          ; preds = %if.else3, %if.then2
 ; CHECK: %[[gep0:.*]] = getelementptr inbounds i1, i1* %[[load]], i64 0
 ; CHECK: store i1 %[[phi]], i1* %[[gep0]], align 4
 
-; CHECK: %[[gep1:.*]] = getelementptr inbounds i1, i1* %[[load]], i64 0
-; CHECK: store i1 %[[phi]], i1* %[[gep1]], align 4
+; Check that store instructions are hoisted.
+; CHECK-NOT: store
\ No newline at end of file