Use dyn_cast, add test.

Author: john-brawn-arm

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1849,8 +1849,8 @@ Instruction *InstCombinerImpl::visitFPTrunc(FPTruncInst &FPT) {
   if (Op && Op->hasOneUse()) {
     IRBuilder<>::FastMathFlagGuard FMFG(Builder);
     FastMathFlags FMF = FPT.getFastMathFlags();
-    if (isa<FPMathOperator>(Op))
-      FMF &= Op->getFastMathFlags();
+    if (auto *FPMO = dyn_cast<FPMathOperator>(Op))
+      FMF &= FPMO->getFastMathFlags();
     Builder.setFastMathFlags(FMF);
 
     if (match(Op, m_FNeg(m_Value(X)))) {

llvm/test/Transforms/InstCombine/fpcast.ll

@@ -150,6 +150,39 @@ define half @test4_unary_fneg-mixed-fast-2(float %a) {
   ret half %c
 }
 
+define <2 x half> @test4_unary_fneg-vec-fast(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc fast <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg fast <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg fast <2 x float> %a
+  %c = fptrunc fast <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
+define <2 x half> @test4_unary_fneg-vec-mixed-fast-1(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-mixed-fast-1(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg <2 x float> %a
+  %c = fptrunc fast <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
+define <2 x half> @test4_unary_fneg-vec-mixed-fast-2(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-mixed-fast-2(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg fast <2 x float> %a
+  %c = fptrunc <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
 define half @test5(float %a, float %b, float %c) {
 ; CHECK-LABEL: @test5(
 ; CHECK-NEXT:    [[D:%.*]] = fcmp ogt float [[A:%.*]], [[B:%.*]]