https://bugs.llvm.org/show_bug.cgi?id=37211
Bug ID: 37211
Summary: [IndVarSimplify] wrong code
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: pauls...@linux.vnet.ibm.com
CC: llvm-bugs@lists.llvm.org
Created attachment 20212
--> https://bugs.llvm.org/attachment.cgi?id=20212&action=edit
reduced testcase
This loop:
lbl_1806: ; preds = %lbl_1806, %entry
%d.0 = phi i16 [ 0, %entry ], [ %dec, %lbl_1806 ]
%dec = add i16 %d.0, -1
%conv2 = mul i16 %dec, %dec
%tobool = icmp eq i16 %conv2, 0
br i1 %tobool, label %if.end, label %lbl_1806
if.end: ; preds = %lbl_1806
%dec.lcssa = phi i16 [ %dec, %lbl_1806 ]
%conv2.lcssa = phi i16 [ %conv2, %lbl_1806 ]
%conv = sext i16 %dec.lcssa to i32
-> *** IR Dump After Induction Variable Simplification ***
; Loop:
lbl_1806: ; preds = %lbl_1806, %entry
%d.0 = phi i16 [ 0, %entry ], [ %dec, %lbl_1806 ]
%dec = add i16 %d.0, -1
%conv2 = mul i16 %dec, %dec
%tobool = icmp eq i16 %conv2, 0
br i1 %tobool, label %if.end, label %lbl_1806
; Exit blocks
if.end: ; preds = %lbl_1806
%conv = sext i16 0 to i32
After the loop, %conv is now sext of constant 0 instead of %dec. My guess is
that IndVarSimplify has thought that the loop must exit when 'mul i16
%dec, %dec' is 0, so therefore %dec is always zero after the loop. However,
since %dec is i16, this happens also when it is -256, and 0 is therefore not
the correct constant after the loop in this case.
bin/clang -w -O3 -march=z13 ./wrong0.i -o ./a.out
Note: this disappears with '-mllvm -disable-licm-promotion'
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