GVN: propagate fcmp equalities (PR17713)

[spatel]

Summary

Patch based on suggestion in PR17713 ( http://llvm.org/bugs/show_bug.cgi?id=17713 ) and discussion in http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-January/080314.html .

This just handles the simple case of propagating FP values along edges; there are still a lot of other cases (eg http://llvm.org/bugs/show_bug.cgi?id=17683 ) that need work.

[ArchDRobison]

Looks correct to me. (The minimalist in me asks if there is a shorter way to write 2.000000e+00?)

• Arch

[spatel]

In D6911#107388, @ArchDRobison wrote:

Looks correct to me. (The minimalist in me asks if there is a shorter way to write 2.000000e+00?)

Thanks, Arch! I can change the IR inputs to plain "2.0", but I'm not aware of a way to change the output (CHECK) formatting.

[pete]

lib/Transforms/Scalar/GVN.cpp

2188 ↗

(On Diff #17963)

I think you need a test case which verifies (positive and negative) cases of a floating point compare here. Looks like a ugt can prove an ole is false for example.

The rest of the changes LGTM if you add tests for these.

[spatel]

Added test cases for other FP comparisons. Tests based on existing integer tests.
Minimized IR: "2.00000+00" --> "2.0".

[pete]

Thanks. LGTM

[spatel]

Thanks, Pete! Checked in at r225660.

llvm/trunk/lib/Transforms/Scalar/GVN.cpp

if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
       Worklist.push_back(std::make_pair(A, RHS));
       Worklist.push_back(std::make_pair(B, RHS));
       continue;
     }
 
     // If we are propagating an equality like "(A == B)" == "true" then also
     // propagate the equality A == B.  When propagating a comparison such as
     // "(A >= B)" == "true", replace all instances of "A < B" with "false".
-    if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
+    if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) {
       Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
 
       // If "A == B" is known true, or "A != B" is known false, then replace
       // A with B everywhere in the scope.
       if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
           (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
         Worklist.push_back(std::make_pair(Op0, Op1));
 
+      // Handle the floating point versions of equality comparisons too.
+      if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) ||
+          (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE))
+        Worklist.push_back(std::make_pair(Op0, Op1));
+
       // If "A >= B" is known true, replace "A < B" with false everywhere.
       CmpInst::Predicate NotPred = Cmp->getInversePredicate();
       Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
       // Since we don't have the instruction "A < B" immediately to hand, work out
       // the value number that it would have and use that to find an appropriate
       // instruction (if any).
       uint32_t NextNum = VN.getNextUnusedValueNumber();
       uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);

llvm/trunk/test/Transforms/GVN/condprop.ll

 ; CHECK: ret i1 false
   ret i1 %cmp2
 
 different:
 ; CHECK: ret i1 false
   ret i1 %cmp3
 }
 
+; CHECK-LABEL: @test6_fp(
+define i1 @test6_fp(float %x, float %y) {
+  %cmp2 = fcmp une float %x, %y
+  %cmp = fcmp oeq float %x, %y
+  %cmp3 = fcmp oeq float  %x, %y
+  br i1 %cmp, label %same, label %different
+
+same:
+; CHECK: ret i1 false
+  ret i1 %cmp2
+
+different:
+; CHECK: ret i1 false
+  ret i1 %cmp3
+}
+
 ; CHECK-LABEL: @test7(
 define i1 @test7(i32 %x, i32 %y) {
   %cmp = icmp sgt i32 %x, %y
   br i1 %cmp, label %same, label %different
 
 same:
   %cmp2 = icmp sle i32 %x, %y
 ; CHECK: ret i1 false
   ret i1 %cmp2
 
 different:
   %cmp3 = icmp sgt i32 %x, %y
 ; CHECK: ret i1 false
   ret i1 %cmp3
 }
 
+; CHECK-LABEL: @test7_fp(
+define i1 @test7_fp(float %x, float %y) {
+  %cmp = fcmp ogt float %x, %y
+  br i1 %cmp, label %same, label %different
+
+same:
+  %cmp2 = fcmp ule float %x, %y
+; CHECK: ret i1 false
+  ret i1 %cmp2
+
+different:
+  %cmp3 = fcmp ogt float %x, %y
+; CHECK: ret i1 false
+  ret i1 %cmp3
+}
+
 ; CHECK-LABEL: @test8(
 define i1 @test8(i32 %x, i32 %y) {
   %cmp2 = icmp sle i32 %x, %y
   %cmp = icmp sgt i32 %x, %y
   %cmp3 = icmp sgt i32 %x, %y
   br i1 %cmp, label %same, label %different
 
 same:
 ; CHECK: ret i1 false
   ret i1 %cmp2
 
 different:
 ; CHECK: ret i1 false
   ret i1 %cmp3
 }
 
+; CHECK-LABEL: @test8_fp(
+define i1 @test8_fp(float %x, float %y) {
+  %cmp2 = fcmp ule float %x, %y
+  %cmp = fcmp ogt float %x, %y
+  %cmp3 = fcmp ogt float %x, %y
+  br i1 %cmp, label %same, label %different
+
+same:
+; CHECK: ret i1 false
+  ret i1 %cmp2
+
+different:
+; CHECK: ret i1 false
+  ret i1 %cmp3
+}
+
 ; PR1768
 ; CHECK-LABEL: @test9(
 define i32 @test9(i32 %i, i32 %j) {
   %cmp = icmp eq i32 %i, %j
   br i1 %cmp, label %cond_true, label %ret
 
 cond_true:
   %diff = sub i32 %i, %j

llvm/trunk/test/Transforms/GVN/edge.ll

 bb1:
   br label %bb2
 bb2:
   %zed = icmp eq i8* null, %x
   call void @g(i1 %zed)
 ; CHECK: call void @g(i1 %y)
   ret void
 }
+
+define double @fcmp_oeq(double %x, double %y) {
+entry:
+  %cmp = fcmp oeq double %y, 2.0
+  br i1 %cmp, label %if, label %return
+
+if:
+  %div = fdiv double %x, %y
+  br label %return
+
+return:
+  %retval.0 = phi double [ %div, %if ], [ %x, %entry ]
+  ret double %retval.0
+
+; CHECK-LABEL: define double @fcmp_oeq(
+; CHECK: %div = fdiv double %x, 2.000000e+00
+}
+
+define double @fcmp_une(double %x, double %y) {
+entry:
+  %cmp = fcmp une double %y, 2.0
+  br i1 %cmp, label %return, label %else
+
+else:
+  %div = fdiv double %x, %y
+  br label %return
+
+return:
+  %retval.0 = phi double [ %div, %else ], [ %x, %entry ]
+  ret double %retval.0
+
+; CHECK-LABEL: define double @fcmp_une(
+; CHECK: %div = fdiv double %x, 2.000000e+00
+}
+