[SimplifyCFG] propagate branch metadata when creating select (retry r268550 / r268751 with possible fix)

Retrying r268550/r268751 which were reverted at r268577/r268765 due a memory sanitizer failure.
I have not been able to reproduce that failure, but I've taken another guess at fixing
the problem in this version of the patch and will watch for another failure.

Original commit message:
Unlike earlier similar fixes, we need to recalculate the branch weights
in this case.

Differential Revision: http://reviews.llvm.org/D19674

llvm-svn: 268767

1 files changed, 39 insertions, 8 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll
index ae32809395e..359f21a75ab 100644
--- a/llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ b/llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -412,22 +412,48 @@ return:
   ret i32 %retval.0
 }
 
-; The 1st select should have branch weights equal to the 1st branch.
-; The 2nd select should have freshly calculated branch weights.
+; The selects should have freshly calculated branch weights.
 
 define i32 @SimplifyCondBranchToCondBranch(i1 %cmpa, i1 %cmpb) {
 ; CHECK-LABEL: @SimplifyCondBranchToCondBranch(
 ; CHECK-NEXT:  block1:
-; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 %cmpb, %cmpa
-; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 %cmpb, i32 0, i32 2
-; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !12
+; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 %cmpa, %cmpb
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 %cmpa, i32 0, i32 2, !prof !12
+; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !13
 ; CHECK-NEXT:    ret i32 [[OUTVAL]]
 ;
 block1:
-  br i1 %cmpb, label %block3, label %block2, !prof !0
+  br i1 %cmpa, label %block3, label %block2, !prof !13
 
 block2:
-  br i1 %cmpa, label %block3, label %exit, !prof !2
+  br i1 %cmpb, label %block3, label %exit, !prof !14
+
+block3:
+  %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
+  br label %exit
+
+exit:
+  %outval = phi i32 [ %cowval, %block3 ], [ 1, %block2 ]
+  ret i32 %outval
+}
+
+; Swap the operands of the compares to verify that the weights update correctly.
+
+define i32 @SimplifyCondBranchToCondBranchSwap(i1 %cmpa, i1 %cmpb) {
+; CHECK-LABEL: @SimplifyCondBranchToCondBranchSwap(
+; CHECK-NEXT:  block1:
+; CHECK-NEXT:    [[CMPA_NOT:%.*]] = xor i1 %cmpa, true
+; CHECK-NEXT:    [[CMPB_NOT:%.*]] = xor i1 %cmpb, true
+; CHECK-NEXT:    [[BRMERGE:%.*]] = or i1 [[CMPA_NOT]], [[CMPB_NOT]]
+; CHECK-NEXT:    [[DOTMUX:%.*]] = select i1 [[CMPA_NOT]], i32 0, i32 2, !prof !14
+; CHECK-NEXT:    [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !15
+; CHECK-NEXT:    ret i32 [[OUTVAL]]
+;
+block1:
+  br i1 %cmpa, label %block2, label %block3, !prof !13
+
+block2:
+  br i1 %cmpb, label %exit, label %block3, !prof !14
 
 block3:
   %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
@@ -452,6 +478,8 @@ exit:
 !10 = !{!"branch_weights", i32 672646, i32 21604207}
 !11 = !{!"branch_weights", i32 6960, i32 21597248}
 !12 = !{!"these_are_not_the_branch_weights_you_are_looking_for", i32 3, i32 5}
+!13 = !{!"branch_weights", i32 2, i32 3}
+!14 = !{!"branch_weights", i32 4, i32 7}
 
 ; CHECK: !0 = !{!"branch_weights", i32 5, i32 11}
 ; CHECK: !1 = !{!"branch_weights", i32 1, i32 5}
@@ -467,5 +495,8 @@ exit:
 ;; treat the weight as an unsigned integer.
 ; CHECK: !10 = !{!"branch_weights", i32 112017436, i32 -735157296}
 ; CHECK: !11 = !{!"branch_weights", i32 3, i32 5}
-; CHECK: !12 = !{!"branch_weights", i32 14, i32 10}
+; CHECK: !12 = !{!"branch_weights", i32 22, i32 12}
+; CHECK: !13 = !{!"branch_weights", i32 34, i32 21}
+; CHECK: !14 = !{!"branch_weights", i32 33, i32 14}
+; CHECK: !15 = !{!"branch_weights", i32 47, i32 8}