[llvm] r179493 - Reorders two transforms that collide with each other

[David Majnemer]

Author: majnemer
Date: Sun Apr 14 16:15:43 2013
New Revision: 179493

URL: http://llvm.org/viewvc/llvm-project?rev=179493&view=rev
Log:
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

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll
    llvm/trunk/test/Transforms/InstCombine/load-cmp.ll
    llvm/trunk/test/Transforms/InstCombine/or.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=179493&r1=179492&r2=179493&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Sun Apr 14 16:15:43 2013
@@ -1547,14 +1547,6 @@ Value *InstCombiner::FoldOrOfICmps(ICmpI
     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(ICmpI
         }
       }
 
+      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

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=179493&r1=179492&r2=179493&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Sun Apr 14 16:15:43 2013
@@ -964,3 +964,15 @@ define i1 @icmp_and_shl_neg_eq_0(i32 %A,
   %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
+}

Modified: llvm/trunk/test/Transforms/InstCombine/load-cmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/load-cmp.ll?rev=179493&r1=179492&r2=179493&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/load-cmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/load-cmp.ll Sun Apr 14 16:15:43 2013
@@ -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
 }
 

Modified: llvm/trunk/test/Transforms/InstCombine/or.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/or.ll?rev=179493&r1=179492&r2=179493&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/or.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/or.ll Sun Apr 14 16:15:43 2013
@@ -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
 }