This is a follow-on of D37211.
D37211 eliminates a compare instruction if two conditional branches can be made based on the one compare instruction, e.g.
if (a == 0) { ... }
else if (a < 0) { ... }
This patch extends this optimization to support partially redundant cases, which often happen in while loops.
For example, one compare instruction is moved from the loop body into the preheader by this optimization in the following example.
do {
if (a == 0) dummy1();
a = func(a);
} while (a > 0);
Differential Revision: https://reviews.llvm.org/D38236
llvm-svn: 314390
If multiple conditional branches are executed based on the same comparison, we can execute multiple conditional branches based on the result of one comparison on PPC. For example,
if (a == 0) { ... }
else if (a < 0) { ... }
can be executed by one compare and two conditional branches instead of two pairs of a compare and a conditional branch.
This patch identifies a code sequence of the two pairs of a compare and a conditional branch and merge the compares if possible.
To maximize the opportunity, we do canonicalization of code sequence before merging compares.
For the above example, the input for this pass looks like:
cmplwi r3, 0
beq 0, .LBB0_3
cmpwi r3, -1
bgt 0, .LBB0_4
So, before merging two compares, we canonicalize it as
cmpwi r3, 0 ; cmplwi and cmpwi yield same result for beq
beq 0, .LBB0_3
cmpwi r3, 0 ; greather than -1 means greater or equal to 0
bge 0, .LBB0_4
The generated code should be
cmpwi r3, 0
beq 0, .LBB0_3
bge 0, .LBB0_4
Differential Revision: https://reviews.llvm.org/D37211
llvm-svn: 312514
Hiroshi Inoue