From: David Majnemer <david.majnemer@gmail.com>
Date: Sun, 14 Apr 2013 21:15:43 +0000 (+0000)
Subject: Reorders two transforms that collide with each other
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=024d943bca85ee0b6bc1b9e5f13ec5276f16c13d;p=oota-llvm.git

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179493 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index a7f01494874..ec75dd2e042 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/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/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 74adbba42b4..c912a576c3d 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/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/test/Transforms/InstCombine/load-cmp.ll b/test/Transforms/InstCombine/load-cmp.ll
index d88188e4109..869215cb58d 100644
--- a/test/Transforms/InstCombine/load-cmp.ll
+++ b/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/test/Transforms/InstCombine/or.ll b/test/Transforms/InstCombine/or.ll
index bde2a54048a..7226bd93996 100644
--- a/test/Transforms/InstCombine/or.ll
+++ b/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
 }