[InstCombine] Relax shamt assertion in fsh fold

Allow the result of the comparison to contain poison elements,
which happens if one of the elements in the input vector is
poison.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -1979,8 +1979,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       if (ModuloC != ShAmtC)
         return replaceOperand(*II, 2, ModuloC);
 
-      assert(ConstantExpr::getICmp(ICmpInst::ICMP_UGT, WidthC, ShAmtC) ==
-                 ConstantInt::getTrue(CmpInst::makeCmpResultType(Ty)) &&
+      assert(match(ConstantExpr::getICmp(ICmpInst::ICMP_UGT, WidthC, ShAmtC),
+                   m_One()) &&
              "Shift amount expected to be modulo bitwidth");
 
       // Canonicalize funnel shift right by constant to funnel shift left. This

llvm/test/Transforms/InstCombine/rotate.ll

@@ -147,6 +147,17 @@ define <2 x i32> @rotr_v2i32_constant_nonsplat_undef0(<2 x i32> %x) {
   ret <2 x i32> %r
 }
 
+define <2 x i32> @rotr_v2i32_constant_nonsplat_poison0(<2 x i32> %x) {
+; CHECK-LABEL: @rotr_v2i32_constant_nonsplat_poison0(
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 poison, i32 19>)
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %shl = shl <2 x i32> %x, <i32 poison, i32 19>
+  %shr = lshr <2 x i32> %x, <i32 15, i32 13>
+  %r = or <2 x i32> %shl, %shr
+  ret <2 x i32> %r
+}
+
 define <2 x i32> @rotr_v2i32_constant_nonsplat_undef1(<2 x i32> %x) {
 ; CHECK-LABEL: @rotr_v2i32_constant_nonsplat_undef1(
 ; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 17, i32 0>)