From 00abcd3da0f36a88fb3c73586a59d782c35e17a6 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sat, 18 Aug 2012 20:06:47 +0000
Subject: [PATCH] InstCombine: Add a couple of fabs identities for comparing
 with 0.0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162174 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineCompares.cpp       | 39 +++++++++
 test/Transforms/InstCombine/fcmp.ll           | 82 +++++++++++++++++++
 2 files changed, 121 insertions(+)

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index bdd310e97f6..3fc1357eae0 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -17,6 +17,7 @@
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetLibraryInfo.h"
 #include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/PatternMatch.h"
@@ -2985,6 +2986,44 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
                 return Res;
         }
         break;
+      case Instruction::Call: {
+        CallInst *CI = cast<CallInst>(LHSI);
+        LibFunc::Func Func;
+        // Various optimization for fabs compared with zero.
+        if (RHSC->isNullValue() && CI->hasOneUse() &&
+            TLI->getLibFunc(CI->getCalledFunction()->getName(), Func) &&
+            TLI->has(Func)) {
+          if (Func == LibFunc::fabs || Func == LibFunc::fabsf ||
+              Func == LibFunc::fabsl) {
+            switch (I.getPredicate()) {
+            default: break;
+            // fabs(x) < 0 --> false
+            case FCmpInst::FCMP_OLT:
+              return ReplaceInstUsesWith(I, Builder->getFalse());
+            // fabs(x) > 0 --> x != 0
+            case FCmpInst::FCMP_OGT:
+              return new FCmpInst(FCmpInst::FCMP_ONE, CI->getArgOperand(0),
+                                  RHSC);
+            // fabs(x) <= 0 --> x == 0
+            case FCmpInst::FCMP_OLE:
+              return new FCmpInst(FCmpInst::FCMP_OEQ, CI->getArgOperand(0),
+                                  RHSC);
+            // fabs(x) >= 0 --> !isnan(x)
+            case FCmpInst::FCMP_OGE:
+              return new FCmpInst(FCmpInst::FCMP_ORD, CI->getArgOperand(0),
+                                  RHSC);
+            // fabs(x) == 0 --> x == 0
+            // fabs(x) != 0 --> x != 0
+            case FCmpInst::FCMP_OEQ:
+            case FCmpInst::FCMP_UEQ:
+            case FCmpInst::FCMP_ONE:
+            case FCmpInst::FCMP_UNE:
+              return new FCmpInst(I.getPredicate(), CI->getArgOperand(0),
+                                  RHSC);
+            }
+          }
+        }
+      }
       }
   }
 
diff --git a/test/Transforms/InstCombine/fcmp.ll b/test/Transforms/InstCombine/fcmp.ll
index d08cbf574a2..82fef484a02 100644
--- a/test/Transforms/InstCombine/fcmp.ll
+++ b/test/Transforms/InstCombine/fcmp.ll
@@ -69,3 +69,85 @@ define float @test8(float %x) nounwind readnone optsize ssp {
 ; CHECK: @test8
 ; CHECK-NEXT: fcmp olt float %x, 0.000000e+00
 }
+
+declare double @fabs(double) nounwind readnone
+
+define i32 @test9(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp olt double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test9
+; CHECK-NOT: fabs
+; CHECK: ret i32 0
+}
+
+define i32 @test10(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp ole double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test10
+; CHECK-NOT: fabs
+; CHECK: fcmp oeq double %a, 0.000000e+00
+}
+
+define i32 @test11(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp ogt double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test11
+; CHECK-NOT: fabs
+; CHECK: fcmp one double %a, 0.000000e+00
+}
+
+define i32 @test12(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp oge double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test12
+; CHECK-NOT: fabs
+; CHECK: fcmp ord double %a, 0.000000e+00
+}
+
+define i32 @test13(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp une double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test13
+; CHECK-NOT: fabs
+; CHECK: fcmp une double %a, 0.000000e+00
+}
+
+define i32 @test14(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp oeq double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test14
+; CHECK-NOT: fabs
+; CHECK: fcmp oeq double %a, 0.000000e+00
+}
+
+define i32 @test15(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp one double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test15
+; CHECK-NOT: fabs
+; CHECK: fcmp one double %a, 0.000000e+00
+}
+
+define i32 @test16(double %a) nounwind {
+  %call = tail call double @fabs(double %a) nounwind
+  %cmp = fcmp ueq double %call, 0.000000e+00
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+; CHECK: @test16
+; CHECK-NOT: fabs
+; CHECK: fcmp ueq double %a, 0.000000e+00
+}