https://llvm.org/bugs/show_bug.cgi?id=31557
Bug ID: 31557
Summary: Missed induction variable optimization
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: car...@google.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Compile the following code with options
--target=powerpc64le-grtev4-linux-gnu -m64 -O2 -mvsx -mcpu=power8
extern void bar(int);
void foo(const int* p, int n) {
for (int j = 0; j < n; ++j) {
int k = p[j];
bar(k);
}
}
I got:
clrldi 30, 4, 32
addi 4, 3, -4
.p2align 5
.LBB0_2: # %for.body
# =>This Inner Loop Header: Depth=1
lwa 3, 4(4)
addi 29, 4, 4
bl _Z3bari
nop
addi 30, 30, -1
mr 4, 29
cmpldi 30, 0
bne 0, .LBB0_2
Var j is an induction variable, it is only used to index an array, so it can be
optimized away, like following
clrldi 30, 4, 32
sldi 30, 30, 2 // *
add 30, 30, 4 // *
addi 4, 3, -4
.p2align 5
.LBB0_2: # %for.body
# =>This Inner Loop Header: Depth=1
lwa 3, 4(4)
addi 29, 4, 4
bl _Z3bari
nop
// addi 30, 30, -1
mr 4, 29
cmpld 30, 29 // *
bne 0, .LBB0_2
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