first step to fixing PR8642: don't fold away empty basic blocks

which have trapping constant exprs in them due to PHI nodes.
Eliminating them can cause the constant expr to be evalutated
on new paths if the input edges are critical.

llvm-svn: 122164

1 files changed, 31 insertions, 0 deletions

diff --git a/llvm/test/Transforms/CodeGenPrepare/basic.ll b/llvm/test/Transforms/CodeGenPrepare/basic.ll
new file mode 100644
index 00000000000..04b4f34bc33
--- /dev/null
+++ b/llvm/test/Transforms/CodeGenPrepare/basic.ll
@@ -0,0 +1,31 @@
+; RUN: opt -codegenprepare %s -S | FileCheck %s
+; PR8642
+
+%0 = type <{ %1, %1 }>
+%1 = type { i8, i8, i8, i8 }
+
+@g_2 = global %0 <{ %1 { i8 1, i8 0, i8 0, i8 undef }, %1 { i8 2, i8 0, i8 0, i8 undef } }>, align 4
+@g_4 = global %1 { i8 3, i8 0, i8 0, i8 undef }, align 4
+
+; CGP shouldn't fold away the empty cond.false.i block, because the constant
+; expr that will get dropped into it could trap.
+define i16 @test1(i8** %argv, i1 %c) nounwind ssp {
+entry:
+  br i1 %c, label %cond.end.i, label %cond.false.i
+
+cond.false.i:                                     ; preds = %entry
+  br label %foo.exit
+
+cond.end.i:                                       ; preds = %entry
+  store i8* null, i8** %argv
+  br label %foo.exit
+
+foo.exit:                                         ; preds = %cond.end.i, %cond.false.i
+  %call1 = phi i16 [ trunc (i32 srem (i32 1, i32 zext (i1 icmp eq (%1* bitcast (i8* getelementptr inbounds (%0* @g_2, i64 0, i32 1, i32 0) to %1*), %1* @g_4) to i32)) to i16), %cond.false.i ], [ 1, %cond.end.i ]
+  ret i16 %call1
+  
+; CHECK: @test1
+; CHECK: cond.false.i:
+; CHECK-NEXT:  br label %foo.exit
+}
+