Fix big shift constant folding

[chfast]

Summary

Constant folding for shift IR instructions ignores all bits above 32 of second argument (shift amount). Because of that, some undef results are not recognized and APInt can raise an assert failure if second argument has more than 64 bits.

[chfast]

How can I find reviewers for the change?

[chfast]

Is there anyone willing to review this?

[chfast]

Better fix (as suggested by nicholas) and test file

[majnemer]

LGTM

[chfast]

My first LGTM, thanks. What should I do with the patch now? Phabricator requires action from me.

[chfast]

Can someone apply this patch to the trunk?

I accidentally closed the review playing with arc.

[majnemer]

Will do.

test/Transforms/ConstProp/shift.ll

+; RUN: opt < %s -constprop -S | FileCheck %s
+
+; CHECK-LABEL: shift_undef_65
+define void @shift_undef_65(i65* %p) {
+  %r1 = lshr i65 2, 18446744073709551617
+  ; CHECK: store i65 undef, %p
+  store i65 %r1, i65* %p
+
+  %r2 = ashr i65 4, 18446744073709551617
+  ; CHECK: store i65 undef, %p
+  store i65 %r2, i65* %p
+
+  %r3 = shl i65 1, 18446744073709551617
+  ; CHECK: store i65 undef, %p
+  store i65 %r3, i65* %p
+
+  ret void
+}
+
+; CHECK-LABEL: shift_undef_256
+define void @shift_undef_256(i256* %p) {
+  %r1 = lshr i256 2, 18446744073709551617
+  ; CHECK: store i256 undef, %p
+  store i256 %r1, i256* %p
+
+  %r2 = ashr i256 4, 18446744073709551618
+  ; CHECK: store i256 undef, %p
+  store i256 %r2, i256* %p
+
+  %r3 = shl i256 1, 18446744073709551619
+  ; CHECK: store i256 undef, %p
+  store i256 %r3, i256* %p
+
+  ret void
+}
+
+; CHECK-LABEL: shift_undef_511
+define void @shift_undef_511(i511* %p) {
+  %r1 = lshr i511 -1, 1208925819614629174706276 ; 2^80 + 100
+  ; CHECK: store i511 undef, %p
+  store i511 %r1, i511* %p
+
+  %r2 = ashr i511 -2, 1208925819614629174706200
+  ; CHECK: store i511 undef, %p
+  store i511 %r2, i511* %p
+
+  %r3 = shl i511 -3, 1208925819614629174706180
+  ; CHECK: store i511 undef, %p
+  store i511 %r3, i511* %p
+
+  ret void
+}