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From 24429cc95657332e3953a21581d3220884da3d75 Mon Sep 17 00:00:00 2001
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From: Siddhesh Poyarekar <siddhesh@sourceware.org>
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Date: Wed, 8 May 2019 22:14:00 +0530
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Subject: [PATCH] arm: Fix up condition codes for conditional arithmetic insn
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When an arithmetic instruction such as add or sub are combined with a
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subsequent compare with zero, its following conditional branch code
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needs fixing up. This is necessary because one could generate an add
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with a subtract of the negative but such a substitution, while correct
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on its own, will change the effect on condition flags since while
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addition of two positive numbers may signal an overflow, addition of a
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positive and a negative number may not. So if earlier the condition
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code was GE, it needs to be fixed up to PL to remain correct.
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We did that for bit operations but not for arithmetic, so do that now.
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---
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src/lj_asm_arm.h | 38 ++++++++++++++++++++------------------
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1 file changed, 20 insertions(+), 18 deletions(-)
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diff --git a/src/lj_asm_arm.h b/src/lj_asm_arm.h
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index 37bfa40f..e585b4c2 100644
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--- a/src/lj_asm_arm.h
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+++ b/src/lj_asm_arm.h
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@@ -1412,13 +1412,28 @@ static void asm_intop(ASMState *as, IRIns *ir, ARMIns ai)
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emit_dn(as, ai^m, dest, left);
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}
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-static void asm_intop_s(ASMState *as, IRIns *ir, ARMIns ai)
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+static ARMIns maybe_drop_zero_cmp(ASMState *as, ARMIns ai)
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{
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- if (as->flagmcp == as->mcp) { /* Drop cmp r, #0. */
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+ if (as->flagmcp == as->mcp) { /* Try to drop cmp r, #0. */
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+ uint32_t cc = (as->mcp[1] >> 28);
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as->flagmcp = NULL;
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- as->mcp++;
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- ai |= ARMI_S;
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+ if (cc <= CC_NE) {
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+ as->mcp++;
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+ ai |= ARMI_S;
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+ } else if (cc == CC_GE) {
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+ *++as->mcp ^= ((CC_GE^CC_PL) << 28);
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+ ai |= ARMI_S;
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+ } else if (cc == CC_LT) {
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+ *++as->mcp ^= ((CC_LT^CC_MI) << 28);
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+ ai |= ARMI_S;
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+ } /* else: other conds don't work with bit ops. */
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}
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+ return ai;
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+}
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+
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+static void asm_intop_s(ASMState *as, IRIns *ir, ARMIns ai)
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+{
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+ ai = maybe_drop_zero_cmp(as, ai);
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asm_intop(as, ir, ai);
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}
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@@ -1514,20 +1529,7 @@ static void asm_neg(ASMState *as, IRIns *ir)
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static void asm_bitop(ASMState *as, IRIns *ir, ARMIns ai)
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{
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- if (as->flagmcp == as->mcp) { /* Try to drop cmp r, #0. */
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- uint32_t cc = (as->mcp[1] >> 28);
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- as->flagmcp = NULL;
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- if (cc <= CC_NE) {
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- as->mcp++;
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- ai |= ARMI_S;
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- } else if (cc == CC_GE) {
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- *++as->mcp ^= ((CC_GE^CC_PL) << 28);
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- ai |= ARMI_S;
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- } else if (cc == CC_LT) {
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- *++as->mcp ^= ((CC_LT^CC_MI) << 28);
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- ai |= ARMI_S;
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- } /* else: other conds don't work with bit ops. */
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- }
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+ ai = maybe_drop_zero_cmp(as, ai);
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if (ir->op2 == 0) {
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Reg dest = ra_dest(as, ir, RSET_GPR);
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uint32_t m = asm_fuseopm(as, ai, ir->op1, RSET_GPR);
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--
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2.21.0
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