From 1fae19555797cad0af7db788a30dd4cc2bc63f6c Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sun, 14 Apr 2013 21:15:43 +0000
Subject: [PATCH] Reorders two transforms that collide with each other

One performs: (X == 13 | X == 14) -> X-13 <u 2
The other: (A == C1 || A == C2) -> (A & ~(C1 ^ C2)) == C1

The problem is that there are certain values of C1 and C2 that
trigger both transforms but the first one blocks out the second,
this generates suboptimal code.

Reordering the transforms should be better in every case and
allows us to do interesting stuff like turn:
  %shr = lshr i32 %X, 4
  %and = and i32 %shr, 15
  %add = add i32 %and, -14
  %tobool = icmp ne i32 %add, 0

into:
  %and = and i32 %X, 240
  %tobool = icmp ne i32 %and, 224

llvm-svn: 179493
---
 llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp | 16 ++++++++--------
 llvm/test/Transforms/InstCombine/icmp.ll                | 12 ++++++++++++
 llvm/test/Transforms/InstCombine/load-cmp.ll            |  4 ++--
 llvm/test/Transforms/InstCombine/or.ll                  |  6 +++---
 4 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index a7f0149..ec75dd2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1547,14 +1547,6 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
     switch (RHSCC) {
     default: llvm_unreachable("Unknown integer condition code!");
     case ICmpInst::ICMP_EQ:
-      if (LHSCst == SubOne(RHSCst)) {
-        // (X == 13 | X == 14) -> X-13 <u 2
-        Constant *AddCST = ConstantExpr::getNeg(LHSCst);
-        Value *Add = Builder->CreateAdd(Val, AddCST, Val->getName()+".off");
-        AddCST = ConstantExpr::getSub(AddOne(RHSCst), LHSCst);
-        return Builder->CreateICmpULT(Add, AddCST);
-      }
-
       if (LHS->getOperand(0) == RHS->getOperand(0)) {
         // if LHSCst and RHSCst differ only by one bit:
         // (A == C1 || A == C2) -> (A & ~(C1 ^ C2)) == C1
@@ -1568,6 +1560,14 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
         }
       }
 
+      if (LHSCst == SubOne(RHSCst)) {
+        // (X == 13 | X == 14) -> X-13 <u 2
+        Constant *AddCST = ConstantExpr::getNeg(LHSCst);
+        Value *Add = Builder->CreateAdd(Val, AddCST, Val->getName()+".off");
+        AddCST = ConstantExpr::getSub(AddOne(RHSCst), LHSCst);
+        return Builder->CreateICmpULT(Add, AddCST);
+      }
+
       break;                         // (X == 13 | X == 15) -> no change
     case ICmpInst::ICMP_UGT:         // (X == 13 | X u> 14) -> no change
     case ICmpInst::ICMP_SGT:         // (X == 13 | X s> 14) -> no change
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 74adbba..c912a57 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -964,3 +964,15 @@ define i1 @icmp_and_shl_neg_eq_0(i32 %A, i32 %B) {
   %cmp = icmp eq i32 %and, 0
   ret i1 %cmp
 }
+
+; CHECK: @icmp_add_and_shr_ne_0
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 %X, 240
+; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 [[AND]], 224
+; CHECK-NEXT: ret i1 [[CMP]]
+define i1 @icmp_add_and_shr_ne_0(i32 %X) {
+  %shr = lshr i32 %X, 4
+  %and = and i32 %shr, 15
+  %add = add i32 %and, -14
+  %tobool = icmp ne i32 %add, 0
+  ret i1 %tobool
+}
diff --git a/llvm/test/Transforms/InstCombine/load-cmp.ll b/llvm/test/Transforms/InstCombine/load-cmp.ll
index d88188e..869215c 100644
--- a/llvm/test/Transforms/InstCombine/load-cmp.ll
+++ b/llvm/test/Transforms/InstCombine/load-cmp.ll
@@ -100,8 +100,8 @@ define i1 @test8(i32 %X) {
   %S = icmp eq i16 %R, 0
   ret i1 %S
 ; CHECK: @test8
-; CHECK-NEXT: add i32 %X, -8
-; CHECK-NEXT: icmp ult i32 {{.*}}, 2
+; CHECK-NEXT: and i32 %X, -2
+; CHECK-NEXT: icmp eq i32 {{.*}}, 8
 ; CHECK-NEXT: ret i1
 }
 
diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index bde2a54..7226bd9 100644
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -178,12 +178,12 @@ define i1 @test18(i32 %A) {
 define i1 @test19(i32 %A) {
         %B = icmp eq i32 %A, 50
         %C = icmp eq i32 %A, 51
-        ;; (A-50) < 2
+        ;; (A&-2) == 50
         %D = or i1 %B, %C
         ret i1 %D
 ; CHECK: @test19
-; CHECK: add i32
-; CHECK: icmp ult 
+; CHECK: and i32
+; CHECK: icmp eq 
 ; CHECK: ret i1
 }
 
-- 
2.7.4