[MergedLoadStoreMotion] Don't transform across may-throw calls

It is unsafe to hoist a load before a function call which may throw, the
throw might prevent a pointer dereference.

Likewise, it is unsafe to sink a store after a call which may throw.
The caller might be able to observe the difference.

This fixes PR27858.

llvm-svn: 270828

2 files changed, 58 insertions, 1 deletions

diff --git a/llvm/test/Transforms/InstMerge/exceptions.ll b/llvm/test/Transforms/InstMerge/exceptions.ll
new file mode 100644
index 00000000000..8564215e72a
--- /dev/null
+++ b/llvm/test/Transforms/InstMerge/exceptions.ll
@@ -0,0 +1,57 @@
+; RUN: opt -basicaa -memdep -mldst-motion -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@r = common global i32 0, align 4
+@s = common global i32 0, align 4
+
+; CHECK-LABEL: define void @test1(
+define void @test1(i1 %cmp, i32* noalias %p) {
+entry:
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  call void @may_throw()
+  %arrayidx = getelementptr inbounds i32, i32* %p, i64 1
+  %0 = load i32, i32* %arrayidx, align 4
+  store i32 %0, i32* @r, align 4
+  br label %if.end
+; CHECK:       call void @may_throw()
+; CHECK-NEXT:  %[[gep:.*]] = getelementptr inbounds i32, i32* %p, i64 1
+; CHECK-NEXT:  %[[load:.*]] = load i32, i32* %[[gep]], align 4
+; CHECK-NEXT:  store i32 %[[load]], i32* @r, align 4
+
+if.else:                                          ; preds = %entry
+  %arrayidx1 = getelementptr inbounds i32, i32* %p, i64 1
+  %1 = load i32, i32* %arrayidx1, align 4
+  store i32 %1, i32* @s, align 4
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+; CHECK-LABEL: define void @test2(
+define void @test2(i1 %cmp, i32* noalias %p) {
+entry:
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %arrayidx = getelementptr inbounds i32, i32* %p, i64 1
+  store i32 1, i32* %arrayidx, align 4
+  call void @may_throw()
+; CHECK:       %[[gep:.*]] = getelementptr inbounds i32, i32* %p, i64 1
+; CHECK-NEXT:  store i32 1, i32* %[[gep]], align 4
+; CHECK-NEXT:  call void @may_throw()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %arrayidx1 = getelementptr inbounds i32, i32* %p, i64 1
+  store i32 2, i32* %arrayidx1, align 4
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+declare void @may_throw()
diff --git a/llvm/test/Transforms/InstMerge/st_sink_no_barrier_call.ll b/llvm/test/Transforms/InstMerge/st_sink_no_barrier_call.ll
index 0ad90f8581e..c2da0f3d0ec 100644
--- a/llvm/test/Transforms/InstMerge/st_sink_no_barrier_call.ll
+++ b/llvm/test/Transforms/InstMerge/st_sink_no_barrier_call.ll
@@ -33,7 +33,7 @@ if.else:                                          ; preds = %entry
   %p3 = getelementptr inbounds %struct.node, %struct.node* %node.017, i32 0, i32 6
   ; CHECK-NOT: store i32
   store i32 %add, i32* %p3, align 4
-  call i32 @foo(i32 5)				  ;not a barrier
+  call i32 @foo(i32 5) nounwind				  ;not a barrier
   br label %if.end
 
 ; CHECK: if.end