Subzero: Make sure register preferences obey register class constraints.

The bug was first spotted in the optimized gl_Color4ub() from spec2k's mesa. The lowering sequences for fptosi and fptoui with i8 or i16 include "mov T_2, T_1" where T_1 and T_2 may have different integer types, and the statement: T_2->setPreferredRegister(T_1, true); If T_2's type is i8 and T_1 is assigned a register that has no 8-bit version, then T_2 gets an unsuitable register. The fix is to honor RegisterOverlap only when RegMask allows. It's hard to construct a good test for this, since it depends heavily on register allocation decisions, which will change over time. BUG= none R=jvoung@chromium.org Review URL: https://codereview.chromium.org/544713002

Subzero: Make sure register preferences obey register class constraints.
dd7b846c · Jim Stichnoth · cabfa304 · dd7b846c
Commit dd7b846c authored Sep 04, 2014 by Jim Stichnoth
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IceRegAlloc.cpp src/IceRegAlloc.cpp +1 -0

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--- a/src/IceRegAlloc.cpp
+++ b/src/IceRegAlloc.cpp
@@ -233,6 +233,7 @@ void LinearScan::scan(const llvm::SmallBitVector &RegMaskFull) {
                                                      : Variable::NoRegister;
    bool AllowedToOverlap = Cur.Var->getRegisterOverlap() &&
                            PreferReg != Variable::NoRegister &&
+                            RegMask[PreferReg] &&
                            !PrecoloredUnhandled[PreferReg];
    if (PreferReg != Variable::NoRegister &&
        (AllowedToOverlap || Free[PreferReg])) {