From 493e57de01ecabc7af76a64cf39992d12efffca0 Mon Sep 17 00:00:00 2001 From: James Molloy Date: Mon, 26 Oct 2015 14:10:46 +0000 Subject: [ValueTracking] Extend r251146 to catch a fairly common case Even though we may not know the value of the shifter operand, it's possible we know the shifter operand is non-zero. This can allow us to infer more known bits - for example: %1 = load %p !range {1, 5} %2 = shl %q, %1 We don't know %1, but we do know that it is nonzero so %2[0] is known zero, and importantly %2 is known non-zero. Calling isKnownNonZero is nontrivially expensive so use an Optional to run it lazily and cache its result. llvm-svn: 251294 --- llvm/test/Analysis/ValueTracking/knownnonzero-shift.ll | 13 +++++++++++++ 1 file changed, 13 insertions(+) create mode 100644 llvm/test/Analysis/ValueTracking/knownnonzero-shift.ll (limited to 'llvm/test') diff --git a/llvm/test/Analysis/ValueTracking/knownnonzero-shift.ll b/llvm/test/Analysis/ValueTracking/knownnonzero-shift.ll new file mode 100644 index 00000000000..e59d19cc2e2 --- /dev/null +++ b/llvm/test/Analysis/ValueTracking/knownnonzero-shift.ll @@ -0,0 +1,13 @@ +; RUN: opt -instsimplify -S < %s | FileCheck %s + +; CHECK-LABEL: @test +define i1 @test(i8 %p, i8* %pq) { + %q = load i8, i8* %pq, !range !0 ; %q is known nonzero; no known bits + %1 = shl i8 %p, %q ; because %q is nonzero, %1[0] is known to be zero. + %2 = and i8 %1, 1 + %x = icmp eq i8 %2, 0 + ; CHECK: ret i1 true + ret i1 %x +} + +!0 = !{ i8 1, i8 5 } -- cgit v1.2.3