[PATCH] D150074: InstCombine: Handle shrinking fneg with fpext source

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: jcranmer-intel, foad, kpn, sepavloff, andrew.w.kaylor.
Herald added subscribers: StephenFan, hiraditya.
Herald added a project: All.
arsenm requested review of this revision.
Herald added a subscriber: wdng.
Herald added a project: LLVM.

This would have regressed when the fsub special case was dropped


https://reviews.llvm.org/D150074

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/double-float-shrink-2.ll


Index: llvm/test/Transforms/InstCombine/double-float-shrink-2.ll
===================================================================
--- llvm/test/Transforms/InstCombine/double-float-shrink-2.ll
+++ llvm/test/Transforms/InstCombine/double-float-shrink-2.ll
@@ -737,4 +737,51 @@
   ret float %F
 }
 
+define float @test_shrink_intrin_fneg_double_src(double %D) {
+; CHECK-LABEL: @test_shrink_intrin_fneg_double_src(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[D:%.*]] to float
+; CHECK-NEXT:    [[F:%.*]] = fneg float [[TMP1]]
+; CHECK-NEXT:    ret float [[F]]
+;
+  %E = fneg double %D
+  %F = fptrunc double %E to float
+  ret float %F
+}
+
+define <2 x float> @test_shrink_intrin_fneg_v2f64_src(<2 x double> %D) {
+; CHECK-LABEL: @test_shrink_intrin_fneg_v2f64_src(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x double> [[D:%.*]] to <2 x float>
+; CHECK-NEXT:    [[F:%.*]] = fneg <2 x float> [[TMP1]]
+; CHECK-NEXT:    ret <2 x float> [[F]]
+;
+  %E = fneg <2 x double> %D
+  %F = fptrunc <2 x double> %E to <2 x float>
+  ret <2 x float> %F
+}
+
+; Make sure fast math flags are preserved
+define float @test_shrink_intrin_fneg_nnan_double_src(double %D) {
+; CHECK-LABEL: @test_shrink_intrin_fneg_nnan_double_src(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[D:%.*]] to float
+; CHECK-NEXT:    [[F:%.*]] = fneg nnan float [[TMP1]]
+; CHECK-NEXT:    ret float [[F]]
+;
+  %E = fneg nnan double %D
+  %F = fptrunc double %E to float
+  ret float %F
+}
+
+define float @test_shrink_intrin_fneg_double_src_multi_use(double %D, ptr %ptr) {
+; CHECK-LABEL: @test_shrink_intrin_fneg_double_src_multi_use(
+; CHECK-NEXT:    [[E:%.*]] = fneg double [[D:%.*]]
+; CHECK-NEXT:    store double [[E]], ptr [[PTR:%.*]], align 8
+; CHECK-NEXT:    [[F:%.*]] = fptrunc double [[E]] to float
+; CHECK-NEXT:    ret float [[F]]
+;
+  %E = fneg double %D
+  store double %E, ptr %ptr
+  %F = fptrunc double %E to float
+  ret float %F
+}
+
 ; DBG-VALID: CheckModuleDebugify: PASS
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1729,6 +1729,16 @@
         return CastInst::CreateFPCast(ExactResult, Ty);
       }
     }
+  } else if (auto *UO = dyn_cast<UnaryOperator>(FPT.getOperand(0));
+             UO && UO->hasOneUse()) {
+    switch (UO->getOpcode()) {
+    case Instruction::FNeg: {
+        Value *TruncSrc = Builder.CreateFPTrunc(UO->getOperand(0), Ty);
+        return UnaryOperator::CreateFNegFMF(TruncSrc, UO);
+    }
+    default:
+        break;
+    }
   }
 
   // (fptrunc (fneg x)) -> (fneg (fptrunc x))


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