[PATCH] InstSimplify: The upper bound of X / C was missing a rounding step
David Majnemer
david.majnemer at gmail.com
Mon Jul 14 12:58:41 PDT 2014
Closed by commit rL212976 (authored by @majnemer).
REPOSITORY
rL LLVM
http://reviews.llvm.org/D4502
Files:
llvm/trunk/lib/Analysis/InstructionSimplify.cpp
llvm/trunk/test/Transforms/InstSimplify/compare.ll
Index: llvm/trunk/test/Transforms/InstSimplify/compare.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/compare.ll
+++ llvm/trunk/test/Transforms/InstSimplify/compare.ll
@@ -913,3 +913,14 @@
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[DIV]], -1073741824
; CHECK-NEXT: ret i1 [[CMP]]
}
+
+define i1 @icmp_sdiv_pr20288(i64 %a) {
+ %div = sdiv i64 %a, -8589934592
+ %cmp = icmp ne i64 %div, 1073741824
+ ret i1 %cmp
+
+; CHECK-LABEL: @icmp_sdiv_pr20288
+; CHECK-NEXT: [[DIV:%.*]] = sdiv i64 %a, -8589934592
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[DIV]], 1073741824
+; CHECK-NEXT: ret i1 [[CMP]]
+}
Index: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp
@@ -1964,7 +1964,15 @@
APInt Val = CI2->getValue().abs();
if (!Val.isMinValue()) {
Lower = IntMin.sdiv(Val);
- Upper = IntMax.sdiv(Val) + 1;
+ APInt Rem;
+ APInt::sdivrem(IntMax, Val, Upper, Rem);
+ // We may need to round the result of the INT_MAX / CI2 calculation up
+ // if we see that the division was not exact.
+ if (Rem.isMinValue())
+ Upper = Upper + 1;
+ else
+ Upper = Upper + 2;
+ assert(Upper != Lower && "Upper part of range has wrapped!");
}
} else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {
// 'lshr x, CI2' produces [0, UINT_MAX >> CI2].
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