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update and consolidate the load pre notes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90050 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1116,6 +1116,8 @@ later.
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//===---------------------------------------------------------------------===//
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[STORE SINKING]
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Store sinking: This code:
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void f (int n, int *cond, int *res) {
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@ -1171,6 +1173,8 @@ This is GCC PR38204.
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//===---------------------------------------------------------------------===//
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[STORE SINKING]
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GCC PR37810 is an interesting case where we should sink load/store reload
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into the if block and outside the loop, so we don't reload/store it on the
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non-call path.
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@ -1198,7 +1202,7 @@ we don't sink the store. We need partially dead store sinking.
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//===---------------------------------------------------------------------===//
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[LOAD PRE with NON-AVAILABLE ADDRESS]
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[LOAD PRE CRIT EDGE SPLITTING]
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GCC PR37166: Sinking of loads prevents SROA'ing the "g" struct on the stack
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leading to excess stack traffic. This could be handled by GVN with some crazy
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@ -1217,63 +1221,58 @@ bb3: ; preds = %bb1, %bb2, %bb
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%11 is partially redundant, an in BB2 it should have the value %8.
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GCC PR33344 is a similar case.
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GCC PR33344 and PR35287 are similar cases.
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//===---------------------------------------------------------------------===//
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[LOAD PRE]
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There are many load PRE testcases in testsuite/gcc.dg/tree-ssa/loadpre* in the
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GCC testsuite. There are many pre testcases as ssa-pre-*.c
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GCC testsuite, ones we don't get yet are (checked through loadpre25):
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[CRIT EDGE BREAKING]
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loadpre3.c predcom-4.c
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[PRE OF READONLY CALL]
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loadpre5.c
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[TURN SELECT INTO BRANCH]
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loadpre14.c loadpre15.c
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actually a conditional increment: loadpre18.c loadpre19.c
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//===---------------------------------------------------------------------===//
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[SCALAR PRE]
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There are many PRE testcases in testsuite/gcc.dg/tree-ssa/ssa-pre-*.c in the
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GCC testsuite.
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//===---------------------------------------------------------------------===//
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There are some interesting cases in testsuite/gcc.dg/tree-ssa/pred-comm* in the
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GCC testsuite. For example, predcom-1.c is:
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GCC testsuite. For example, we get the first example in predcom-1.c, but
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miss the second one:
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for (i = 2; i < 1000; i++)
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fib[i] = (fib[i-1] + fib[i - 2]) & 0xffff;
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unsigned fib[1000];
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unsigned avg[1000];
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which compiles into:
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__attribute__ ((noinline))
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void count_averages(int n) {
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int i;
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for (i = 1; i < n; i++)
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avg[i] = (((unsigned long) fib[i - 1] + fib[i] + fib[i + 1]) / 3) & 0xffff;
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}
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bb1: ; preds = %bb1, %bb1.thread
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%indvar = phi i32 [ 0, %bb1.thread ], [ %0, %bb1 ]
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%i.0.reg2mem.0 = add i32 %indvar, 2
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%0 = add i32 %indvar, 1 ; <i32> [#uses=3]
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%1 = getelementptr [1000 x i32]* @fib, i32 0, i32 %0
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%2 = load i32* %1, align 4 ; <i32> [#uses=1]
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%3 = getelementptr [1000 x i32]* @fib, i32 0, i32 %indvar
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%4 = load i32* %3, align 4 ; <i32> [#uses=1]
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%5 = add i32 %4, %2 ; <i32> [#uses=1]
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%6 = and i32 %5, 65535 ; <i32> [#uses=1]
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%7 = getelementptr [1000 x i32]* @fib, i32 0, i32 %i.0.reg2mem.0
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store i32 %6, i32* %7, align 4
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%exitcond = icmp eq i32 %0, 998 ; <i1> [#uses=1]
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br i1 %exitcond, label %return, label %bb1
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which compiles into two loads instead of one in the loop.
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This is basically:
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LOAD fib[i+1]
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LOAD fib[i]
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STORE fib[i+2]
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predcom-2.c is the same as predcom-1.c
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instead of handling this as a loop or other xform, all we'd need to do is teach
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load PRE to phi translate the %0 add (i+1) into the predecessor as (i'+1+1) =
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(i'+2) (where i' is the previous iteration of i). This would find the store
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which feeds it.
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predcom-2.c is apparently the same as predcom-1.c
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predcom-3.c is very similar but needs loads feeding each other instead of
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store->load.
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predcom-4.c seems the same as the rest.
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//===---------------------------------------------------------------------===//
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Other simple load PRE cases:
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35287 [LPRE crit edge splitting]
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34677 (licm does this, LPRE crit edge)
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llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as | opt -mem2reg -simplifycfg -gvn | llvm-dis
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//===---------------------------------------------------------------------===//
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Type based alias analysis:
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@ -1305,7 +1304,7 @@ Interesting missed case because of control flow flattening (should be 2 loads):
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26629
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With: llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as |
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opt -mem2reg -gvn -instcombine | llvm-dis
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we miss it because we need 1) GEP PHI TRAN, 2) CRIT EDGE 3) MULTIPLE DIFFERENT
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we miss it because we need 1) CRIT EDGE 2) MULTIPLE DIFFERENT
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VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
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//===---------------------------------------------------------------------===//
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