Consider (x == -1) unlikely in BranchProbabilityInfo

This adds another heuristic to BPI, similar to the existing heuristic that
considers (x == 0) unlikely to be true. As suggested in the PACT'98 paper by
Deitrich, Cheng, and Hwu, -1 is often used to indicate an invalid index, and
equality comparisons with -1 are also unlikely to succeed. Local
experimentation supports this hypothesis: This yields a 1-2% speedup in the
test-suite sqlite benchmark on the PPC A2 core, with no significant
regressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193855 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 39 insertions, 0 deletions

diff --git a/test/Analysis/BranchProbabilityInfo/basic.ll b/test/Analysis/BranchProbabilityInfo/basic.ll
index c6e1bde81d..05cb31dca0 100644
--- a/test/Analysis/BranchProbabilityInfo/basic.ll
+++ b/test/Analysis/BranchProbabilityInfo/basic.ll
@@ -173,3 +173,42 @@ exit:
   %ret = phi i32 [ %val4, %then ], [ %val3, %else ]
   ret i32 %ret
 }
+
+define i32 @zero1(i32 %i, i32 %a, i32 %b) {
+; CHECK: Printing analysis {{.*}} for function 'zero1'
+entry:
+  %cond = icmp eq i32 %i, 0
+  br i1 %cond, label %then, label %else
+; CHECK: edge entry -> then probability is 12 / 32
+; CHECK: edge entry -> else probability is 20 / 32
+
+then:
+  br label %exit
+
+else:
+  br label %exit
+
+exit:
+  %result = phi i32 [ %a, %then ], [ %b, %else ]
+  ret i32 %result
+}
+
+define i32 @zero2(i32 %i, i32 %a, i32 %b) {
+; CHECK: Printing analysis {{.*}} for function 'zero2'
+entry:
+  %cond = icmp ne i32 %i, -1
+  br i1 %cond, label %then, label %else
+; CHECK: edge entry -> then probability is 20 / 32
+; CHECK: edge entry -> else probability is 12 / 32
+
+then:
+  br label %exit
+
+else:
+  br label %exit
+
+exit:
+  %result = phi i32 [ %a, %then ], [ %b, %else ]
+  ret i32 %result
+}
+