Fix SCEV overly optimistic back edge taken count for multi-exit loops.

Fixes PR11375: Different results for 'clang++ huh.cpp'...


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144746 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 0 deletions

diff --git a/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll b/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll
new file mode 100644
index 0000000..c74d04e
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/2011-11-15-multiexit.ll
@@ -0,0 +1,40 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+;
+; Prior to the fix for PR11375, indvars would replace %firstIV with a
+; loop-invariant gep computed in the preheader. This was incorrect
+; because it was based on the minimum "ExitNotTaken" count. If the
+; final loop test is skipped (odd number of elements) then the early
+; exit would be taken and the loop invariant value would be incorrect.
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-darwin"
+
+; CHECK: if.end:
+; CHECK: phi i32* [ %first.lcssa, %early.exit ]
+define i32 @test(i32* %first, i32* %last) uwtable ssp {
+entry:
+  br i1 undef, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  br i1 undef, label %if.end, label %do.body
+
+do.body:                                          ; preds = %if.else, %if.then
+  %firstIV = phi i32* [ %incdec.ptr2, %if.else ], [ %first, %if.then ]
+  %incdec.ptr1 = getelementptr inbounds i32* %firstIV, i64 1
+  %cmp1 = icmp eq i32* %incdec.ptr1, %last
+  br i1 %cmp1, label %early.exit, label %if.else
+
+if.else:                                        ; preds = %do.body
+  %incdec.ptr2 = getelementptr inbounds i32* %firstIV, i64 2
+  %cmp2 = icmp eq i32* %incdec.ptr2, %last
+  br i1 %cmp2, label %if.end, label %do.body
+
+early.exit:
+  %first.lcssa = phi i32* [ %firstIV, %do.body ]
+  br label %if.end
+
+if.end:
+  %tmp = phi i32* [ %first.lcssa, %early.exit ], [ %first, %if.then ], [ %first, %entry ], [ undef, %if.else ]
+  %val = load i32* %tmp
+  ret i32 %val
+}