[InstCombine] Gating select arithmetic optimization.

These changes faciliate positive behavior for arithmetic based select
expressions that match its translation criteria, keeping code size gated to
neutral or improved scenarios.

Patch by Michael Berg <michael_c_berg@apple.com>!

Differential Revision: https://reviews.llvm.org/D38263

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314320 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 60db2ddb63c103503dcc37fb1d8d4b11a52113bd..2271e219d0fbf84c39414f3e05096fdedb729084 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -731,6 +731,7 @@ Value *InstCombiner::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
   Value *SI = nullptr;
   if (match(LHS, m_Select(m_Value(A), m_Value(B), m_Value(C))) &&
       match(RHS, m_Select(m_Specific(A), m_Value(D), m_Value(E)))) {
+    bool SelectsHaveOneUse = LHS->hasOneUse() && RHS->hasOneUse();
     BuilderTy::FastMathFlagGuard Guard(Builder);
     if (isa<FPMathOperator>(&I))
       Builder.setFastMathFlags(I.getFastMathFlags());
@@ -739,9 +740,9 @@ Value *InstCombiner::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
     Value *V2 = SimplifyBinOp(Opcode, B, D, SQ.getWithInstruction(&I));
     if (V1 && V2)
       SI = Builder.CreateSelect(A, V2, V1);
-    else if (V2)
+    else if (V2 && SelectsHaveOneUse)
       SI = Builder.CreateSelect(A, V2, Builder.CreateBinOp(Opcode, C, E));
-    else if (V1)
+    else if (V1 && SelectsHaveOneUse)
       SI = Builder.CreateSelect(A, Builder.CreateBinOp(Opcode, B, D), V1);
 
     if (SI)

diff --git a/test/Transforms/InstCombine/select_arithmetic.ll b/test/Transforms/InstCombine/select_arithmetic.ll
index d33bbdd1d439edab99edb5458a4f1153a0b51525..8fde7c0807ed75e84601b99f54780cb30481e48e 100644 (file)
--- a/test/Transforms/InstCombine/select_arithmetic.ll
+++ b/test/Transforms/InstCombine/select_arithmetic.ll
@@ -3,17 +3,32 @@
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
 ; Tests folding constants from two similar selects that feed a add
-define float @test1(i1 zeroext %arg) #0 {
+define float @test1a(i1 zeroext %arg) #0 {
   %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
   %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
   %tmp2 = fadd float %tmp, %tmp1
   ret float %tmp2
-; CHECK-LABEL: @test1(
+; CHECK-LABEL: @test1a(
 ; CHECK: %tmp2 = select i1 %arg, float 6.000000e+00, float 1.500000e+01
 ; CHECK-NOT: fadd
 ; CHECK: ret float %tmp2
 }
 
+; Tests folding multiple expression constants from similar selects that feed a adds
+define float @test1b(i1 zeroext %arg) #0 {
+  %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
+  %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
+  %tmp2 = select i1 %arg, float 2.500000e-01, float 4.000000e+00
+  %tmp3 = fadd float %tmp, %tmp1
+  %tmp4 = fadd float %tmp2, %tmp1
+  %tmp5 = fadd float %tmp4, %tmp3
+  ret float %tmp5
+; CHECK-LABEL: @test1b(
+; CHECK: %tmp5 = select i1 %arg, float 7.250000e+00, float 2.800000e+01
+; CHECK-NOT: fadd
+; CHECK: ret float %tmp5
+}
+
 ; Tests folding constants from two similar selects that feed a sub
 define float @test2(i1 zeroext %arg) #0 {
   %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
@@ -38,3 +53,32 @@ define float @test3(i1 zeroext %arg) #0 {
 ; CHECK: ret float %tmp2
 }
 
+declare void @use_float(float)
+
+; Tests folding constants if the selects have multiple uses but
+; we can fold away the binary op with a select.
+define float @test4(i1 zeroext %arg) #0 {
+  %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
+  %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
+  %tmp2 = fmul float %tmp, %tmp1
+  call void @use_float(float %tmp)
+  ret float %tmp2
+; CHECK-LABEL: @test4(
+; CHECK: select i1 %arg, float 5.000000e+00, float 6.000000e+00
+; CHECK-NEXT: select i1 %arg, float 5.000000e+00, float 5.400000e+01
+; CHECK-NEXT: call void @use_float(float %tmp)
+; CHECK: ret float %tmp2
+}
+
+; Tests not folding constants if we cannot fold away any of the selects.
+define float @test5(i1 zeroext %arg, float %div) {
+  %tmp = select i1 %arg, float %div, float 5.000000e+00
+  %mul = fmul contract float %tmp, %tmp
+  call void @use_float(float %tmp)
+  ret float %mul
+; CHECK-LABEL: @test5(
+; CHECK: [[TMP:%.*]] = select i1 %arg, float %div, float 5.000000e+00
+; CHECK-NEXT: [[MUL:%.*]] = fmul contract float [[TMP]], [[TMP]]
+; CHECK-NOT: fmul contract float %div, %div
+; CHECK: ret float [[MUL]]
+}