diff options
| -rw-r--r-- | llvm/lib/CodeGen/CodeGenPrepare.cpp | 3 | ||||
| -rw-r--r-- | llvm/test/Transforms/CodeGenPrepare/X86/select.ll | 29 |
2 files changed, 26 insertions, 6 deletions
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp index 9ba93a956fa..659b0c572fb 100644 --- a/llvm/lib/CodeGen/CodeGenPrepare.cpp +++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp @@ -4568,7 +4568,8 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) { bool VectorCond = !SI->getCondition()->getType()->isIntegerTy(1); // Can we convert the 'select' to CF ? - if (DisableSelectToBranch || OptSize || !TLI || VectorCond) + if (DisableSelectToBranch || OptSize || !TLI || VectorCond || + SI->getMetadata(LLVMContext::MD_unpredictable)) return false; TargetLowering::SelectSupportKind SelectKind; diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/select.ll b/llvm/test/Transforms/CodeGenPrepare/X86/select.ll index 15c0772b144..79b195d21ca 100644 --- a/llvm/test/Transforms/CodeGenPrepare/X86/select.ll +++ b/llvm/test/Transforms/CodeGenPrepare/X86/select.ll @@ -53,7 +53,7 @@ entry: ; CHECK: %div = fdiv float %a, %b ; CHECK: br label %select.end ; CHECK: select.end: -; CHECK: %sel = phi float [ 4.000000e+00, %entry ], [ %div, %select.false.sink ] +; CHECK: %sel = phi float [ 4.000000e+00, %entry ], [ %div, %select.false.sink ] ; CHECK: ret float %sel } @@ -75,20 +75,39 @@ entry: ; CHECK: %div2 = fdiv float %b, %a ; CHECK: br label %select.end ; CHECK: select.end: -; CHECK: %sel = phi float [ %div1, %select.true.sink ], [ %div2, %select.false.sink ] +; CHECK: %sel = phi float [ %div1, %select.true.sink ], [ %div2, %select.false.sink ] ; CHECK: ret float %sel } +; But if the select is marked unpredictable, then don't turn it into a branch. + +define float @unpredictable_select(float %a, float %b) { +; CHECK-LABEL: @unpredictable_select( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[DIV:%.*]] = fdiv float %a, %b +; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float %a, 1.000000e+00 +; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], float [[DIV]], float 2.000000e+00, !unpredictable !0 +; CHECK-NEXT: ret float [[SEL]] +; +entry: + %div = fdiv float %a, %b + %cmp = fcmp ogt float %a, 1.0 + %sel = select i1 %cmp, float %div, float 2.0, !unpredictable !0 + ret float %sel +} + +!0 = !{} + ; An 'fadd' is not too expensive, so it's ok to speculate. define float @fadd_no_sink(float %a, float %b) { %add = fadd float %a, %b %cmp = fcmp ogt float 6.0, %a - %sel = select i1 %cmp, float %add, float 7.0 + %sel = select i1 %cmp, float %add, float 7.0 ret float %sel ; CHECK-LABEL: @fadd_no_sink( -; CHECK: %sel = select i1 %cmp, float %add, float 7.0 +; CHECK: %sel = select i1 %cmp, float %add, float 7.0 } ; Possible enhancement: sinkability is only calculated with the direct @@ -104,7 +123,7 @@ entry: ret float %sel ; CHECK-LABEL: @fdiv_no_sink( -; CHECK: %sel = select i1 %cmp, float %add, float 8.0 +; CHECK: %sel = select i1 %cmp, float %add, float 8.0 } ; Do not transform the CFG if the select operands may have side effects. |
