[CodeExtractor] Fix sinking of allocas with multiple bitcast uses (PR42451)

An alloca which can be sunk into the extraction region may have more
than one bitcast use. Move these uses along with the alloca to prevent
use-before-def.

Testing: check-llvm, stage2 build of clang

Fixes llvm.org/PR42451.

Differential Revision: https://reviews.llvm.org/D64463

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365660 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/CodeExtractor.cpp b/lib/Transforms/Utils/CodeExtractor.cpp
index f70b09c7cada3ec52680d3a0a447ae5691696b36..27064d590bbfa19d1fb42a0c96cc93fa3b8b2111 100644 (file)
--- a/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/lib/Transforms/Utils/CodeExtractor.cpp
@@ -519,18 +519,20 @@ void CodeExtractor::findAllocas(ValueSet &SinkCands, ValueSet &HoistCands,
       if (Bitcasts.empty())
         continue;
 
-      Instruction *BitcastAddr = Bitcasts.back();
-      const LifetimeMarkerInfo &LMI = BitcastLifetimeInfo.back();
-      assert(LMI.LifeStart &&
-             "Unsafe to sink bitcast without lifetime markers");
-      moveOrIgnoreLifetimeMarkers(LMI);
-      if (!definedInRegion(Blocks, BitcastAddr)) {
-        LLVM_DEBUG(dbgs() << "Sinking bitcast-of-alloca: " << *BitcastAddr
-                          << "\n");
-        SinkCands.insert(BitcastAddr);
-      }
       LLVM_DEBUG(dbgs() << "Sinking alloca (via bitcast): " << *AI << "\n");
       SinkCands.insert(AI);
+      for (unsigned I = 0, E = Bitcasts.size(); I != E; ++I) {
+        Instruction *BitcastAddr = Bitcasts[I];
+        const LifetimeMarkerInfo &LMI = BitcastLifetimeInfo[I];
+        assert(LMI.LifeStart &&
+               "Unsafe to sink bitcast without lifetime markers");
+        moveOrIgnoreLifetimeMarkers(LMI);
+        if (!definedInRegion(Blocks, BitcastAddr)) {
+          LLVM_DEBUG(dbgs() << "Sinking bitcast-of-alloca: " << *BitcastAddr
+                            << "\n");
+          SinkCands.insert(BitcastAddr);
+        }
+      }
     }
   }
 }
@@ -1431,9 +1433,23 @@ Function *CodeExtractor::extractCodeRegion() {
   findInputsOutputs(inputs, outputs, SinkingCands);
 
   // Now sink all instructions which only have non-phi uses inside the region.
-  for (auto *II : SinkingCands)
-    cast<Instruction>(II)->moveBefore(*newFuncRoot,
-                                      newFuncRoot->getFirstInsertionPt());
+  // Group the allocas at the start of the block, so that any bitcast uses of
+  // the allocas are well-defined.
+  AllocaInst *FirstSunkAlloca = nullptr;
+  for (auto *II : SinkingCands) {
+    if (auto *AI = dyn_cast<AllocaInst>(II)) {
+      AI->moveBefore(*newFuncRoot, newFuncRoot->getFirstInsertionPt());
+      if (!FirstSunkAlloca)
+        FirstSunkAlloca = AI;
+    }
+  }
+  assert((SinkingCands.empty() || FirstSunkAlloca) &&
+         "Did not expect a sink candidate without any allocas");
+  for (auto *II : SinkingCands) {
+    if (!isa<AllocaInst>(II)) {
+      cast<Instruction>(II)->moveAfter(FirstSunkAlloca);
+    }
+  }
 
   if (!HoistingCands.empty()) {
     auto *HoistToBlock = findOrCreateBlockForHoisting(CommonExit);

diff --git a/test/Transforms/CodeExtractor/live_shrink_multiple.ll b/test/Transforms/CodeExtractor/live_shrink_multiple.ll
index 9350ca2ef9c8737394a4aebdf7f3c9453fb0bf62..3f4c9472b778823d91bd0f8bc8e5fe2c1b632cd2 100644 (file)
--- a/test/Transforms/CodeExtractor/live_shrink_multiple.ll
+++ b/test/Transforms/CodeExtractor/live_shrink_multiple.ll
@@ -45,9 +45,9 @@ bb:
 ; CHECK-LABEL: define internal void @_Z3foov.1.
 ; CHECK: newFuncRoot:
 ; CHECK-NEXT:  alloca 
+; CHECK-NEXT:  alloca
 ; CHECK-NEXT:  bitcast 
 ; CHECK-NEXT:  call void @llvm.lifetime.start.p0i8
-; CHECK-NEXT:  alloca
 ; CHECK-NEXT:  bitcast 
 ; CHECK-NEXT:  call void @llvm.lifetime.start.p0i8
 ; CHECK:  call void @llvm.lifetime.end.p0i8

diff --git a/test/Transforms/HotColdSplit/sink-multiple-bitcasts-of-allocas-pr42451.ll b/test/Transforms/HotColdSplit/sink-multiple-bitcasts-of-allocas-pr42451.ll
new file mode 100644 (file)
index 0000000..d2f8398
--- /dev/null
+++ b/test/Transforms/HotColdSplit/sink-multiple-bitcasts-of-allocas-pr42451.ll
@@ -0,0 +1,74 @@
+; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=-1 -S < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+@c = common global i32 0, align 4
+@h = common global i32 0, align 4
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #1
+
+declare i32* @m()
+
+; CHECK-LABEL: define void @main()
+; CHECK-NEXT:   %.sroa.4.i = alloca [20 x i8], align 2
+; CHECK-NEXT:   %.sroa.5.i = alloca [6 x i8], align 8
+; CHECK-NEXT:   %1 = bitcast [6 x i8]* %.sroa.5.i to i8*
+
+define void @main() #0 {
+  %.sroa.4.i = alloca [20 x i8], align 2
+  %.sroa.5.i = alloca [6 x i8], align 8
+  %1 = bitcast [6 x i8]* %.sroa.5.i to i8*
+  %2 = load i32, i32* @h, align 4, !tbaa !4
+  %3 = icmp ne i32 %2, 0
+  br i1 %3, label %12, label %4
+
+4:                                                ; preds = %0
+  %5 = call i32* @m() #3
+  %.sroa.4.0..sroa_idx21.i = getelementptr inbounds [20 x i8], [20 x i8]* %.sroa.4.i, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 20, i8* %.sroa.4.0..sroa_idx21.i) #3
+  %.sroa.5.0..sroa_idx16.i = getelementptr inbounds [6 x i8], [6 x i8]* %.sroa.5.i, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 6, i8* %.sroa.5.0..sroa_idx16.i) #3
+  call void @llvm.memset.p0i8.i64(i8* align 2 %.sroa.4.0..sroa_idx21.i, i8 0, i64 20, i1 false) #3
+  call void @llvm.memset.p0i8.i64(i8* align 8 %.sroa.5.0..sroa_idx16.i, i8 0, i64 6, i1 false) #3
+  %6 = load i32, i32* @c, align 4, !tbaa !4
+  %7 = trunc i32 %6 to i16
+  call void @llvm.lifetime.end.p0i8(i64 20, i8* %.sroa.4.0..sroa_idx21.i) #3
+  call void @llvm.lifetime.end.p0i8(i64 6, i8* %.sroa.5.0..sroa_idx16.i) #3
+  call void @llvm.lifetime.start.p0i8(i64 6, i8* %1) #3
+  call void @llvm.memset.p0i8.i64(i8* align 1 %1, i8 3, i64 6, i1 false)
+  br label %8
+
+8:                                                ; preds = %8, %4
+  %.0.i = phi i32 [ 0, %4 ], [ %10, %8 ]
+  %9 = sext i32 %.0.i to i64
+  %10 = add nsw i32 %.0.i, 1
+  %11 = icmp slt i32 %10, 6
+  br i1 %11, label %8, label %l.exit
+
+l.exit:                                           ; preds = %8
+  call void @llvm.lifetime.end.p0i8(i64 6, i8* %1) #3
+  br label %12
+
+12:                                               ; preds = %l.exit, %0
+  %13 = phi i1 [ true, %0 ], [ true, %l.exit ]
+  ret void
+}
+
+attributes #0 = { cold }
+
+!llvm.module.flags = !{!0, !1, !2}
+!llvm.ident = !{!3}
+
+!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 14]}
+!1 = !{i32 1, !"wchar_size", i32 4}
+!2 = !{i32 7, !"PIC Level", i32 2}
+!3 = !{!"Apple clang version 11.0.0 (clang-1100.0.20.17)"}
+!4 = !{!5, !5, i64 0}
+!5 = !{!"int", !6, i64 0}
+!6 = !{!"omnipotent char", !7, i64 0}
+!7 = !{!"Simple C/C++ TBAA"}