Merge pull request JuliaLang#25630 from JuliaLang/kf/llvmunionsplit

Fix performance problem in LLVM JumpThreading

deps/llvm.mk

@@ -462,6 +462,7 @@ $(eval $(call LLVM_PATCH,llvm-PR29010-i386-xmm)) # Remove for 4.0
 $(eval $(call LLVM_PATCH,llvm-3.9.0-D37576-NVPTX-sm_70)) # NVPTX, Remove for 6.0
 $(eval $(call LLVM_PATCH,llvm-D37939-Mem2Reg-Also-handle-memcpy))
 $(eval $(call LLVM_PATCH,llvm-D31524-sovers_4.0)) # Remove for 4.0
+$(eval $(call LLVM_PATCH,llvm-D42262-jumpthreading-not-i1))
 ifeq ($(BUILD_LLVM_CLANG),1)
 $(eval $(call LLVM_PATCH,compiler_rt-3.9-glibc_2.25.90)) # Remove for 5.0
 endif
@@ -488,6 +489,7 @@ $(eval $(call LLVM_PATCH,llvm-Yet-another-fix))
 $(eval $(call LLVM_PATCH,llvm-NVPTX-addrspaces)) # NVPTX
 $(eval $(call LLVM_PATCH,llvm-4.0.0-D37576-NVPTX-sm_70)) # NVPTX, Remove for 6.0
 $(eval $(call LLVM_PATCH,llvm-loadcse-addrspace_4.0))
+$(eval $(call LLVM_PATCH,llvm-D42262-jumpthreading-not-i1))
 ifeq ($(BUILD_LLVM_CLANG),1)
 $(eval $(call LLVM_PATCH,compiler_rt-3.9-glibc_2.25.90)) # Remove for 5.0
 endif
@@ -501,6 +503,7 @@ $(eval $(call LLVM_PATCH,llvm-D34078-vectorize-fdiv))
 $(eval $(call LLVM_PATCH,llvm-5.0-NVPTX-addrspaces)) # NVPTX
 $(eval $(call LLVM_PATCH,llvm-4.0.0-D37576-NVPTX-sm_70)) # NVPTX, Remove for 6.0
 $(eval $(call LLVM_PATCH,llvm-D38765-gvn_5.0)) # Remove for 6.0
+$(eval $(call LLVM_PATCH,llvm-D42262-jumpthreading-not-i1))
 endif # LLVM_VER
 
 # Remove hardcoded OS X requirements in compilter-rt cmake build

deps/patches/llvm-D42262-jumpthreading-not-i1.patch

@@ -0,0 +1,82 @@
+commit 6a311a7a804831fea43cfb2f61322adcb407a1af
+Author: Keno Fischer <[email protected]>
+Date: Thu Jan 18 15:57:05 2018 -0500
+
+ [JumpThreading] Don't restrict cast-traversal to i1
+
+ Summary:
+ In D17663, JumpThreading learned to look trough simple cast instructions,
+ but only if the source of those cast instructions was a phi/cmp i1
+ (in an effort to limit compile time effects). I think this condition
+ is too restrictive. For switches with limited value range, InstCombine
+ will readily introduce an extra `trunc` instruction to a smaller
+ integer type (e.g. from i8 to i2), leaving us in the somewhat perverse
+ situation that jump-threading would work before running instcombine,
+ but not after. Since instcombine produces this pattern, I think we
+ need to consider it canonical and support it in JumpThreading.
+ In general, for limiting recursion, I think the existing restriction
+ to phi and cmp nodes should be sufficient to avoid looking through
+ unprofitable chains of instructions.
+
+ Reviewers: haicheng, gberry, bmakam, mcrosier
+
+ Subscribers: llvm-commits
+
+ Differential Revision: https://reviews.llvm.org/D42262
+
+diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
+index 95c4650..1155e18 100644
+--- a/lib/Transforms/Scalar/JumpThreading.cpp
++++ b/lib/Transforms/Scalar/JumpThreading.cpp
+@@ -647,11 +647,9 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
+ }
+
+ // Handle Cast instructions. Only see through Cast when the source operand is
+- // PHI or Cmp and the source type is i1 to save the compilation time.
++ // PHI or Cmp to save the compilation time.
+ if (CastInst *CI = dyn_cast<CastInst>(I)) {
+ Value *Source = CI->getOperand(0);
+- if (!Source->getType()->isIntegerTy(1))
+- return false;
+ if (!isa<PHINode>(Source) && !isa<CmpInst>(Source))
+ return false;
+ ComputeValueKnownInPredecessors(Source, BB, Result, Preference, CxtI);
+diff --git a/test/Transforms/JumpThreading/basic.ll b/test/Transforms/JumpThreading/basic.ll
+index ce86cba..16e7549 100644
+--- a/test/Transforms/JumpThreading/basic.ll
++++ b/test/Transforms/JumpThreading/basic.ll
+@@ -547,6 +547,34 @@ l5:
+ ; CHECK: }
+ }
+
++define i1 @trunc_switch(i1 %arg) {
++; CHECK-LABEL: @trunc_switch
++top:
++; CHECK: br i1 %arg, label %exitA, label %exitB
++ br i1 %arg, label %common, label %B
++
++B:
++ br label %common
++
++common:
++ %phi = phi i8 [ 2, %B ], [ 1, %top ]
++ %trunc = trunc i8 %phi to i2
++; CHECK-NOT: switch
++ switch i2 %trunc, label %unreach [
++ i2 1, label %exitA
++ i2 -2, label %exitB
++ ]
++
++unreach:
++ unreachable
++
++exitA:
++ ret i1 true
++
++exitB:
++ ret i1 false
++}
++
+ ; CHECK-LABEL: define void @h_con(i32 %p) {
+ define void @h_con(i32 %p) {
+ %x = icmp ult i32 %p, 5