[llvm] [SROA] Propagate no-signed-zeros(nsz) fast-math flag on the phi node using function attribute (PR #83381)

[Sushant Gokhale via llvm-commits]

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@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes='sroa' -S | FileCheck %s
+define double @phi_with_nsz(double %x) "no-signed-zeros-fp-math"="true" {
+; CHECK-LABEL: define double @phi_with_nsz(
+; CHECK-SAME: double [[X:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[FNEG:%.*]] = fneg double [[X]]
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    [[X_ADDR_0:%.*]] = phi nsz double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret double [[X_ADDR_0]]
+entry:
+  %x.addr = alloca double
+  %cmp = fcmp olt double %x, 0.0
+  br i1 %cmp, label %if.then, label %return
+
+if.then:                         ; preds = %entry
+  %fneg = fneg double %x
+  store double %fneg, ptr %x.addr
+  br label %return
+
+return:                          ; preds = %entry,%if.then
+  %retval = load double, ptr %x.addr
+  ret double %retval
+}
+
+define double @phi_without_nsz(double %x) "no-signed-zeros-fp-math"="false" {
+; CHECK-LABEL: define double @phi_without_nsz(
+; CHECK-SAME: double [[X:%.*]]) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[FNEG:%.*]] = fneg double [[X]]
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    [[X_ADDR_0:%.*]] = phi double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret double [[X_ADDR_0]]
+entry:
+  %x.addr = alloca double
+  %cmp = fcmp olt double %x, 0.0
+  br i1 %cmp, label %if.then, label %return
+
+if.then:                         ; preds = %entry
+  %fneg = fneg double %x
+  store double %fneg, ptr %x.addr
+  br label %return
+
+return:                          ; preds = %entry,%if.then
+  %retval = load double, ptr %x.addr
+  ret double %retval
+}
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sushgokh wrote:

why do we need a vector case here? Are you expecting that user starts the pipeline from the vectorization itself and this scalar folding does not happen?

https://github.com/llvm/llvm-project/pull/83381